10th Workshop on Nuclear Level Density and Gamma Strength

18 May 2026, 08:30 → 22 May 2026, 23:10 Europe/Oslo

Auditorium 1 (Helga Engs Hus)

Sunniva Siem (University of Oslo)

The 10th Workshop on Nuclear Level Density and Gamma Strength will be held in-person in Oslo during the last week of May 2026 (18-22 May). The program will consist of invited talks, selected oral contributions from the submitted abstracts and a poster session. The workshop will cover the following topics:

• Nuclear Level Density (NLD)
• Gamma-Ray Strength Function (GSF)
• Applications of NLD and GSF in Astrophysics
• Applications in Fission and Reactor Physics
• Other Related Topics

 

---

 Program

Talks will be either 15 + 5 minutes or 25 +5 minutes

 

 

---

 

Important dates: 

• Abstract submission for talks/posters: 15th of February 19th of February
• Notification of accepted talks/posters: 1st of March
• Registration deadline: 1st of April

---

Organizing committee:

• Ali Al-Adili
• Lauren Bell
• Andreas Görgen
• Henrik Haug
• Johannes Heines
• Vetle Wegner Ingeberg
• Azusa Inoue
• Neeraj Kumar
• Ann-Cecilie Larsen
• Kevin Li
• Maria Markova
• Gøril Mellem
• Wanja Paulsen
• Sunniva Siem

Monday 18 May

08:30 → 09:00 Registration and coffee

09:00 → 11:00 Breakfast session

Convener: Magne Guttormsen (University of Oslo)

09:20 High Flux Nuclear Science: From Medicine to Space Exploration to High Energy Density Physics

The short range of the nuclear force has often been used by nuclear physicists to justify ignoring most of the influence of a high energy density plasma (HEDP) environment on neutron induced nuclear reaction dynamics. However, the recent achievement of Lawson’s criterion [1] and the achievement of target gain >1 at the National Ignition Facility (NIF) [2] has for the first time created a Neutron-rich High Energy Density Plasma (nHEDP) environment where the rate of electromagnetic energy exchange between the nucleus and its external environment becomes comparable to the rate of neutron-induced reactions. The resulting intersection of nuclear and plasma science opens the possibility of studying the interplay between compound nuclear states and its surrounding plasma environment. Furthermore, the extraordinarily high neutron flux in these inertial fusion systems poses significant materials science challenges like those faced by space applications.
In this talk I will present efforts underway in Berkeley to address both the scientific and operational challenges of studying nuclear reactions in HEDP settings. This includes a review of a recent experiment at the BELLA facility at Lawrence Berkeley National Laboratory (LBNL) that showed evidence of plasma-nuclear induced excitations of isomeric states in 80Br [3] and an experimental campaign at the NIF to study the influence of a nHEDP on fission dynamics. I will also discuss how a new experimental capability developed at LBNL to address these issues can also be used to produce copious quantities of the two most promising radionuclides under development for the treatment of cancer via targeted alpha therapy, 225Ac and 212Pb.
This work was supported by the U.S. Department of Energy Offices of High Energy and Nuclear Physics, under Contract No. DEAC02-05CH11231, and by a philanthropic gift from Google LLC.
[1] Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment. H. Abu-Shawareb et al.*. Phys. Rev. Lett. 129, 075001 (2022). https://doi.org/10.1103/PhysRevLett.129.075001
[2] Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment. H. Abu-Shawareb et al. Phys. Rev. Lett. 132, 065102 (2024). https://doi.org/10.1103/PhysRevLett.132.065102
[3] Enhanced isomer population via direct irradiation of solid-density targets using a compact laser-plasma accelerator. Robert E. Jacob et al., Phys. Rev. Lett. 134, 052504 (2025). https://doi.org/10.1103/PhysRevLett.134.052504

Speaker: Prof. Lee Bernstein (UC Berkeley/LBNL)

09:50 Nuclear Level Densities and Photon Strength Functions for Basic Science and Applications

Nuclear level densities (NLD) and photon strength functions (PSF) are essential input parameters for theoretical calculations and evaluations of nuclear reaction data for basic science and a wide range of nuclear applications.
The IAEA Reference Input Parameter Library (RIPL), released in 2009 [1], provided reliable level‑density and photon‑strength‑function models and recommended values widely used in reaction modelling and nuclear data evaluations, forming a foundation for nuclear astrophysics and many nuclear applications. To reflect major advances in experimental techniques, modelling approaches and evaluations over the past decades, the IAEA is coordinating focused research projects that address individual RIPL components.
The CRP on a Photon Strength Function (PSF) reference database [2] produced a comprehensive compilation of experimentally derived strength functions and two recommended global models—one microscopic and one phenomenological—both rigorously validated against PSF and related integral data. Experimental and calculated PSF data are now available through a user-friendly online interface [3]. Follow up activities focus on studying the systematics of the different measured strengths and on performing a data-driven evaluation of the experimental PSFs.
A second CRP, on Updating Nuclear Level Densities for Applications [4], is currently compiling an extensive database of experimentally extracted level densities. The CRP work programme [4] includes re-evaluation of average neutron resonance spacings, development of new global phenomenological and microscopic models, and using theoretical advances to improve our understanding of spin distributions and collective enhancement. All tables, data files, and recommended models will be disseminated across multiple platforms, and a comprehensive final publication will document the full CRP results.
This presentation will provide an overview of both PSF and NLD projects, summarizing achievements so far and highlighting remaining challenges and future needs.

References
[1] R. Capote et al., Nucl. Data Sheets 110 (2009) 3107.
[2] S. Goriely et al., Eur. Phys. J. A (2019) 55:172.
[3] S. Jongile et al., EPJ Web of Conferences 322 (2025) 06005.
[4] S. Hilaire et al., in Summary Report of the 1st Research Coordination Meeting on Nuclear Level Densities, INDC(NDS)-0920, IAEA, September 2025.

Speaker: Paraskevi Dimitriou (International Atomic Energy Agency)

10:20 Isomer Population via the Quasi-Continuum with Laser-Accelerated Electrons

Experiments were performed at the Berkeley Lab Laser Accelerator (BELLA) facility, where $^{81}$Br targets were irradiated using 15 MeV electron beams. The associated bremsstrahlung radiation served as a control for the measurements. The experiments were conducted under a range of spatially and temporally focused and defocused beam conditions, enabling a systematic investigation of their impact on nuclear excitation pathways.

The resulting photonuclear reactions populated both the isomeric and ground states of
$^{80}$Br via feeding from the quasi-continuum. Using the activation technique, combined with high-resolution γ-ray spectroscopy, isomer-to-ground-state population ratios were measured under the different irradiation conditions. The results demonstrate clear dependencies of the isomeric yield ratios on the temporal and spatial characteristics of the electron beam. These measurements provide new insights into the role of the quasi-continuum in isomer population mechanisms and offer important benchmarks for reaction modeling.

The work that will be presented establishes a framework for controlled studies of isomer production using laser-accelerated electron beams and contributes to broader efforts to quantify nuclear excitation and decay pathways.

This material is based upon work supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-05CH11231 and by the US Nuclear Data Program.

Speaker: Mathis Wiedeking (Lawrence Berkeley National Laboratory)

10:40 Average resonance parameters derived from neutron resonances

Average resonance parameters, particularly the average resonance spacing, derived from experimental neutron-resonance data are essential for many nuclear-physics applications, including testing level-density models and normalizing experimental results. Two widely used compilations are the IAEA RIPL-3 database [1] and Said Mughabghab’s Atlas of Neutron Resonances (latest edition 2018) [2]. However, the methodologies and uncertainty treatments used to obtain the published values are not well documented in either source. The IAEA Coordinated Research Project "Updating and Improving Nuclear Level Densities for Applications" (2024–2028) [3] has suggested a new evaluation of these parameters. Preliminary results of this new evaluation will be presented with a special emphasis on reproducibility of the results and on the treatment of different uncertainties.

[1] R. Capote et al., Nucl. Data Sheets 110, 3107 (2009).
[2] S. F. Mughabghab, Atlas of Neutron Resonances: Resonance Properties and Thermal Cross Sections Z=1-60 & Z=61-102 (Elsevier,
Amsterdam, 2018)
[3] https://www.iaea.org/projects/crp/f41034

Speaker: Milan Krticka (Charles University, Prague)

11:00 → 11:30 Coffee

11:30 → 13:00 Midday Session

Convener: Ann-Cecilie Larsen (University of Oslo (NO))

11:30 Theoretical description of the photon strength function and nuclear level densities

Reliable theoretical predictions of nuclear dipole excitations and level densities in the whole nuclear chart are of great interest for different applications, including in particular nuclear astrophysics. We present here our latest calculations of the de-excitation E1 and M1 photon strength functions obtained in the framework of the axially-symmetric deformed quasiparticle random phase approximation (QRPA) based on the finite-range D1M Gogny force. These calculations are compared with photoabsorption strength function as well as available experimental data (including those obtained within the Oslo method). Predictions of the dipole strength function for spherical and deformed nuclei within the valley of stability as well as in the neutron-rich region are discussed. The impact on the total radiative width and radiative neutron capture cross sections will also be presented.

Similarly, based on the same QRPA framework but complemented by the boson expansion method, the nuclear level densities are extracted systematically. This new method to determine energy-, spin- and parity-dependent level densities and its capacity to reproduce experimental data will be presented. A comparison with standard nuclear level densities will also be discussed.

Speaker: Stephane Goriely

26-Oslo-Goriely.pptx

12:00 Detection of γ-ray from laser plasma using nuclear emulsion

In recent years, advances in laser technology have enabled focused intensities on targets to reach up to 10^22~W/cm^2.Within the plasma formed on the target by the laser, ultra-high-density electromagnetic field is generated. High-energy electrons and ions with energies of several tens of MeV have been observed from such laser plasmas, suggesting the possibility that nuclear reactions are induced within the plasma. However, if the granularity is not sufficiently high, the detector cannot perform detailed measurements due to pile-up. This is because reactions in laser plasma occur in extremely short durations and at high densities.
In this study, we aim to establish a γ-ray detection method using nuclear emulsion, which is known for its extremely high granularity. Once established, this method will contribute to a better understanding of phenomena occurring in laser plasma. Furthermore, if laser intensity increases further, it will lead to the development of new research methods that were difficult to perform with conventional acceleration. For example, it will enable the study of nuclear reactions using high-density photons, and under ultra-high electromagnetic field environments, such as inside magnetars.
We analyzed data from an experiment conducted in 2021 using the J-KAREN-P laser at the National Institutes for Quantum Science and Technology (QST), and successfully observed γ-ray events in nuclear emulsion. However, the nuclear emulsions used in this experiment have traditionally been employed in high-energy regions (several GeV and above), such as in cosmic-ray experiments. Therefore, in the typical energy range of nuclear reactions (several tens of MeV), the momentum resolution and detection efficiency may significantly deteriorate. Therefore, we will evaluate the performance of nuclear emulsion at low momentum by analyzing calibration experiments conducted in 2024 using the Electron Linac at the Institute for Chemical Research (ICR).
In this presentation, we will explain the experimental results at QST while comparing them with calibration results at ICR.

Speaker: Toma Hori (RCNP)

オスロ発表資料 English.pdf

オスロ発表資料 English.pptx

12:20 Oslo Method study of the silver isotopic chain: $^{107,109}$Ag from (p,p$^\prime\gamma$) at OCL

Nuclear level densities (NLDs) and $\gamma$-ray strength functions (GSFs) provide key inputs to Hauser-Feshbach calculations and therefore influence reaction rate predictions used in nucleosynthesis modelling and applied studies. Previous Oslo method and complementary measurements in the palladium and cadmium mass region have highlighted characteristic features of the dipole response, including a low-energy enhancement that appears to weaken or vanish, as well as a possible pygmy dipole-resonance strength. These features can significantly affect calculated reaction rates, and therefore further understanding of the evolution of these features is key.

This project aims to extract the NLDs and GSFs of the silver isotopes $^{107}$Ag and $^{109}$Ag below the neutron separation energy using the Oslo method. The talk will present these preliminary results from the first round of a larger campaign of experiments at the Oslo Cyclotron Laboratory, with the goal of characterising features in a large selection of the silver isotopic chain. This campaign will extend Oslo method data to odd-$Z$ nuclei in the palladium-cadmium-tin mass region to investigate the evolution of the pygmy dipole resonance and the low-energy enhancement.

Speaker: Henrik Døvle Andrews (University of Oslo)

Oslo_conference_Henrik_Andrews.pdf

Oslo_conference_Henrik_Andrews.pptx

12:40 Optimized Statistical Property Parameterization using Machine Learning

Nuclear level densities (NLD) and gamma strength functions (gSF) are key parameters used to calculate neutron-capture cross sections where experimental data does not exist. Current Hauser-Feshbach calculations allow for the use of a variety of models for NLD and gSF, ranging from phenomenological to microscopic. Using published experimental data, as well as Hauser-Feshbach calculations performed using TALYS [1], a machine learning model is being developed to improve NLD and gSF model predictions. The Molybdenum isotopic chain was chosen as an initial use case for this development because of the large number of stable isotopes and the amount of available information on statistical properties from previous work. The developed model will be validated against new results from nuclear resonance fluorescence and particle evaporation measurements. Additionally, we plan to test the model using results from upcoming beta-Oslo experiments to demonstrate its effectiveness as we move away from stability. The goal of this work is to improve parameter choices in Hauser-Feshbach calculations and strengthen the foundation for accurate nuclear data evaluations critical to a variety of applications.

Acknowledgement: This work was supported by the Office of Defense Nuclear Nonproliferation Research and Development within the U.S. Department of Energy’s National Nuclear Security Administration.

References:
[1] Koning, A., Hilaire, S., and Goriely, S., (2023) Eur. Phys. J. A 59, 131

Speaker: Stephanie Lyons (Pacific Northwest National Laboratory)

Lyons_OsloMeeting_Systematics.pptx

13:00 → 14:30 Lunch

14:30 → 16:20 Afternoon session

Convener: Luna Pellegri

14:30 Shape method application to 85Kr.

We present the first implementation of the Shape method in inverse kinematics. Traditionally, the Shape method relies on identifiable diagonals in the first generation matrix to extract the shape of the gamma-ray strength function. Our results show that the method works even if no clear diagonals are not identified. We also applied for the first time the Shape method to extract the gamma-ray strength function in the unfolded matrix and same results were obtained as from the first generation matrix.

Speaker: Mhlangano Freedom Nkalanga (University of Johannesburg)

14:50 Impact of octupole deformation on the nuclear electromagnetic response

Reflection-symmetry-breaking nuclear octupole deformation is a phenomenon of significant interest due to its connection with fundamental symmetry considerations ($\mathcal{C}$, $\mathcal{P}$, and $\mathcal{T}$) and its relevance in nuclear structure studies. Substantial experimental evidence indicates that a few nuclei exhibit a pear-like octupole deformation [1], whereas global theoretical studies predict the existence of a dozen or even more such nuclei [2]. Meanwhile, the nuclear electromagnetic response can provide insight into the collective properties of the nucleus, such as deformation [3,4]. However, the impact of octupole deformation on the nuclear electromagnetic response remains less studied and is the focus of the present work.

We have studied the effect of octupole deformation on the nuclear electromagnetic response using nuclear density functional theory (DFT) combined with linear response theory. We employed the Skyrme-Hartree-Fock-Bogoliubov (HFB) model to determine two distinct deformed ground-state solutions for the studied nuclei: one with conserved and the other with broken reflection symmetry. Based on these two HFB ground-state solutions, we performed finite amplitude method (FAM) [5] calculations to solve quasiparticle random phase approximation (QRPA)-type equations and obtain transition strength functions. In the calculations, zero-energy linear and rotational momentum spurious modes associated with the broken translational and rotational symmetries, respectively, were removed where relevant. The resulting transition strength functions and selected sum rules were then compared between the two deformed HFB solutions.

We calculated electric and magnetic transition strength functions for different multipolarities ($E1$, $E2$, $E3$, and $M1$) of expected octupole-deformed even-even nuclei around the actinide region. Our results indicate three key aspects of the effect of octupole deformation on the nuclear electromagnetic response. Firstly, octupole deformation appears to have only a modest impact on the transition strengths in the resonance region. Secondly, at low excitation energies (< 8 MeV) of $M1$ transitions, especially around the expected scissors resonance [4], octupole deformation has a stronger impact on transition strengths. This effect even leads to a violation of the expected correlation [4] between the non-energy weighted sum rule and the quadrupole deformation parameter. Thirdly, our analysis confirms that octupole-deformed solutions can exhibit a significant rotational spurious contribution to the isoscalar $E3$ transition strength (its $K=1^-$ mode), which is consistent with the non-conservation of parity in these solutions. Therefore, both the rotational and linear-momentum spurious modes were removed from the calculated isoscalar $E3$ transition strengths. These results motivate further investigation into the impact of octupole deformation on low-energy $M1$ transitions and highlight the importance of accounting for spurious mode contributions arising from broken parity symmetry.

[1] P. A. Butler. Proc. R. Soc. A 476, 20200202 (2020).
[2] Y. Cao \emph{et al.} Phys. Rev. C 102, 024311 (2020).
[3] B. L. Berman and S. C. Fultz. Rev. Mod. Phys. 47, 713 (1975).
[4] K. Heyde, P. von Neumann-Cosel, and A. Richter. Rev. Mod. Phys. 82, 2365 (2010).
[5] P. Avogadro and T. Nakatsukasa. Phys. Rev. C 84, 014314 (2011).

Speaker: Manu Kanerva (University of Jyväskylä)

15:10 Scissors Mode Strength in the Quasicontinuum

Oslo method and neutron-capture $\gamma$ decay experimenents on heavy deformed nuclei systematically show a resonance-like structure around 2 - 3 MeV in the gamma strength function (GSF) interpreted as the scissors mode in the quasicontinuum. Its $M1$ character has been demonstrated by polarization experiments [1] and its strength may be connected to the low-energy enhancement phenomeon in Oslo-type experiments [2]. One of the longstanding questions is whether the integrated strength differs from the systematics derived from g.s. excitation experiments [3]. A recent compilation shows that experimental results scatter from approximate agreement to about four times the g.s. strength [4].

We have reanalyzed data from a recent Oslo experiment on $^{150}$Nd [5] aiming at a systematic fit of the GSF similar to Ref. [6] to constrain the background from the low-energy tail of the GDR. In the studied excitation energy range of about 4.5 - 7.5 MeV results are independent of initial or final energy consistent with the generalized Brink-Axel hypothesis. However, the absolute strength is 5.9(2) $\mu_N^2$, i.e. about twice the g.s. strength. Possible interpetations in the framework of an angular momentum-projected shell model [7] are discussed.

[1] F. Bello Garrote et al., Phys.Lett. B 834, 137479 (2022)
[2] R. Schwengner et al., Phys. Rev. Lett. 118, 092502 (2017)
[3] K. Heyde et al. Rev. Mod. Phys. 82, 2365 (2010)
[4] F. Pogliano et al., Phys. Rev. C 107, 034605 (2023)
[5] M. Guttormsen et al., Phys. Rev. C 106, 034314 (2022)
[6] M. Markova et al., Phys. Rev. C 109, 054311 (2024)
[7] F.-Q. Chen et al., Phys. Rev. Lett. 134, 082502 (2025)

Speaker: Peter von Neumann-Cosel

2026 Oslo Workshop Scissors Mode in the Quasicontinuum.pdf

15:30 AMiCARE: A FRIPRO International Mobility Project

wanjaPaulsen_10thWorkshopNLDandGSF_2026.pdf

16:30 → 18:30 Poster session

16:30 Production and Biodistribution of Sr-82

I will present my results from my work with Sr-82 that was conducted at LBNL fall 2025. Strontium 82 was produced, chemically separated and injected into mice. The biodistribution of Sr-82 was then measure both using PET scans and collection and gamma counting of organs after the end of the experiment. On the PET scans we can see a clear accumulation in the skeleton and head region, however the measurements of the brain using a HHPGe detector shows no activation of the brain after 10 days.

Speaker: Elise Malmer Martinsen (Univeristy of Oslo)

16:50 Very asymmetric fission yields of U-233(n,f) at LOHENGRIN

In this work we present our work investigating the super assymetric fission mode in $^{233}$U with the LOHENGRIN mass recoil spectrometer. In this poster we will report on preliminary results and the effort made during the experimental campaign conducted in June 2025 and in April 2026.

Speaker: Marius Torsvoll (University of Oslo)

17:10 Toward a Comprehensive Understanding of Big Bang Nucleosynthesis ~ Experimental and Theoretical Approaches ~

In this poster, we present the results of our previous experimental study and discuss a future theoretical approach. The aim of our research is to achieve a comprehensive understanding of the Big Bang Nucleosynthesis (BBN) process and to potentially resolve the Cosmological Lithium Problem (CLP). The CLP is a well-known issue in astrophysics, referring to the overestimation of the primordial $^7\mathrm{Li}$ abundance in standard BBN models compared to astronomical observations.
The experimental approach focuses on measuring the cross section of the $^7\mathrm{Be}(d,p)^8\mathrm{Be}$ reaction, motivated by theoretical suggestions of its important role in the destruction of $^7\mathrm{Be}$ during BBN [1]. The majority of $^7\mathrm{Li}$ nuclei are produced through the electron capture decay of $^7\mathrm{Be}$ ($T_{1/2} = 53.22$ days $= 4.6 \times 10^6$ s). Since $^7\mathrm{Be}$ nuclei are produced within several hundred seconds during BBN, there is a timescale difference of over $10^4$ between the production of $^7\mathrm{Be}$ and the formation of $^7\mathrm{Li}$. This suggests that enhanced destruction of $^7\mathrm{Be}$ during BBN could reduce the final $^7\mathrm{Li}$ abundance, potentially resolving the discrepancy. The measurement of the absolute cross section in the Big Bang energy region ($E_{\mathrm{c.m.}} = 0.1$--$0.4$ MeV) is crucial for understanding nuclear reactions in the primordial universe. We produced a radioactive $^7\mathrm{Be}$ target and measured the $^7\mathrm{Be}(d,p)^8\mathrm{Be}$ reaction cross section at the tandem facility of Kobe University in Japan. A 2.36 MeV proton beam irradiated a natural Li target with a thickness of $30~\mu\mathrm{m}$, producing $^7\mathrm{Be}$ nuclei via the $^7\mathrm{Li}(p,n)^7\mathrm{Be}$ reaction. A total of $2.80 \times 10^{13}$ $^7\mathrm{Be}$ nuclei were produced in the Li host target over two days of irradiation. After target production, a deuteron beam was accelerated to energies of 1.6 and 0.6 MeV to measure the $^7\mathrm{Be}(d,p)^8\mathrm{Be}$ reaction cross section. The outgoing protons were detected using two sets of four-layer silicon detectors placed at scattering angles of 45$^\circ$ and 30$^\circ$. The thick-target analysis method was applied to determine the cross sections. The cross section at the lowest energy of $E_{\mathrm{c.m.}} = 0.12$ MeV was obtained with the highest sensitivity compared to previous data [2,3,4]. The measured $^7\mathrm{Be}(d,p)^8\mathrm{Be}$ cross sections indicate a limited impact on the understanding of the CLP.
In addition, a future theoretical study is outlined, focusing on the exploration of potential resonant contributions in key nuclear reactions. In this approach, nuclear reaction cross sections are parametrized using an external functional form, enabling a flexible inclusion of resonant contributions within the BBN reaction network. This allows us to investigate whether such resonant effects could modify reaction rates relevant to BBN and thereby provide further insight into the CLP.

References
[1] S. Q. Hou et al., Phys. Rev. C 91, 055802 (2015).
[2] R. Kavanagh, Nucl. Phys. 18, 492--501 (1960).
[3] C. Angulo et al., ApJ 630, L105 (2005).
[4] N. Rijal et al., Phys. Rev. Lett. 122, 182701 (2019).

Speaker: Azusa Inoue

17:30 Radiative capture reaction studies at iThemba LABS

The low-energy nuclear astrophysics beamline at the iThemba LABS 3-MV Tandetron facility enables the study of radiative capture reactions using proton and alpha beams. The setup can presently be instrumented with either up to twelve 3″×3″ LaBr₃:Ce detectors or six HPGe detectors (with associated BGO Compton-suppression shields), or with a combination of both detector types. To date, proton beams have primarily been employed for studies of the photon strength function (PSF), which is important not only for calculating nucleosynthesis reaction rates but also for probing the underlying nuclear structure. Experiments using alpha beams have focused on reactions relevant to helium burning in stars.

As is typical for measurements at such low energies, the sensitivity of the experiment is strongly affected by background produced when Rutherford-scattered beam particles interact with nuclei in surrounding hardware rather than in the intended target.

Preliminary results from selected experiments will be presented, together with a discussion of background-mitigation strategies and investigations into the origin of the observed background due to the 19F(p,alpha)16O reaction.

Speaker: Retief Neveling (iThemba LABS, South Africa)

17:50 GEANT4 Microdosimetry Model for PSMA-targeted $^{212}$Pb Induced Cell Damage

Targeted alpha therapy is a new modality of cancer treatment in which alpha-emitters are used to precisely target cancer cells; however the short range of alpha particles makes assessing the actual dose of radiation delivered to the cell challenging. PSMA-targeted $^{212}$Pb radionuclides have previously been clinically investigated for prostate cancer cell lines C4-2, PC3-PIP and PC3-Flu. Clonogenic assays have been performed for different concentrations of radionuclides. In this thesis I will use these experiments as constraints to perform GEANT4 Monte Carlo particle transport simulations. This allows me to investigate energy depositions in different parts of the cell, with special attention to the nucleus, where DNA resides.

Speaker: Oskar Ekeid Idland (Department of Physics, University of Oslo)

18:10 Determination of ground-state decay level width in $^{27}$Al using the temperature-dependent relative self-absorption technique

The first temperature-dependent relative self-absorption (TRSA) measurement was conducted at the Darmstadt High-Intensity Photon Setup (DHIPS) at the superconducting Darmstadt linear electron accelerator (S-DALINAC) on the nucleus $^{27}$Al using a bremsstrahlung photon beam with an endpoint energy of 5.5 MeV. This technique enables the separation of the natural linewidth of the nuclear transition from the Doppler broadening caused by the thermal motion of atom in the solid target. The present work aims to measure the ground-state decay width of the 3957-keV level with high precision. Measurements were performed with and without an absorbing target at three different temperatures: 77 K, 320 K, and 600 K. The technique and its connection to both nuclear and atomic theory will be presented with a discussion of the results.
This work was supported by the DFG under Project-ID 279384907—SFB 1245 and Project-ID 499256822—GRK 2891 “Nuclear Photonics”.

Speaker: Kiriaki Prifti (IKP, TU Darmstadt)

18:10 Extracting isomeric yield ratios of fission fragments

In nuclear fission, a heavy nucleus splits and the fission fragments emerge spinning [2]. The isomeric yield ratio (IYR) i.e. the population frequency of an isomer, is know to be sensitive to the angular momentum of the fragment. Measuring the IYR can therefore give information about the initial sate of the fission fragments.

This work uses a technique to reach short lived isomeric states where the IYR has not been measured before [1]. We study the IYR of the 52ns isomer in $^{130}$Sn, extracted for the fissoning system $^{238}$U(n,f) at two different energies, as well as the 511ns isomer in $^{135}$Te extracted for the fissoning systems $^{232}$Th(n,f) and $^{238}$U(n,f) at two different energies. From looking at how the different fissoning systems affect the IYR, we get more knowledge about what impact the angular momentum generation. The fission code GEF is used in combination with the nuclear decay code TALYS to find the fragment angular momentum from the IYR.

References
[1] D. Gjestvang et al., Phys. Rev C, 108 (2023) 064602.

[2] Wilson, J. N. et al., Nature (London) 590 (2021) 566-570.

Speaker: Henrik Haug

18:10 Extracting the nuclear level density and $\gamma$-ray strength function of $^{90}Zr$

he Nuclear Level Density (NLD) and Gamma-ray strength function (GSF) are important quantities to study as they are inputs into the Hauser-Fesbach statistical model calculations which are used to predict reaction cross-sections. Once experimentally measured they can be used as inputs in codes such as TALYS [1] to calculate/constrain the $(n,\gamma)$ cross-sections. Thus, it is important to experimentally measure the NLD and GSF for as many nuclei as possible as it can help us validate theoretical models which predict reaction rate cross-sections.

An experiment was performed at the Oslo Cyclotron Laboratory using the CATCUS detector array and the $^{90}Zr(p,p'\gamma)^{90}Zr$ reaction was studied. The NLD and GSF for this reaction, below the neutron separation energy, were extracted using the Oslo method . Preliminary results from this analysis are presented here. As $^{90}Zr $ does not have any neutron resonance spacing data available one can use systematics to estimate the neutron resonance spacing or use the shape method [2] to obtain the slope of the GSF and thus the NLD when using the Oslo method. In this work the GSF and thus the NLD have been constrained by the Shape method.
Furthermore, the NLD and GSF from this work have been used to calculate the $^{89}Zr(n,\gamma)^{90}Zr$ and $^{89}Y(p,\gamma)^{90}Zr$ cross-section using TALYS [1].

References
1. A.J. Koning and D. Rochman. “Modern Nuclear Data Evaluation with
the TALYS Code System”. In: Nuclear Data Sheets 113.12 (2012). Spe-
cial Issue on Nuclear Reaction Data, pp. 2841–2934. issn: 0090-3752. doi:
https://doi.org/10.1016/j.nds.2012.11.002. url: https://www.
sciencedirect.com/science/article/pii/S0090375212009.\\relax
2. M. Wiedeking et al. “Independent normalization for γ-ray strength func-
tions: The shape method”. In: Phys. Rev. C 104 (1 2021), p. 014311. doi:
10.1103/PhysRevC.104.014311. url: https://link.aps.org/doi/10.
1103/PhysRevC.104.014311

Speaker: Lauren Bell (University of Oslo)

18:10 Neutronic Analysis of a Hybrid Fuel Cycle Between Maritime and Terrestrial Fluoride-salt-cooled High-temperature Reactors

This study computationally evaluates a hybrid nuclear fuel cycle in which partially depleted fuel pebbles from a compact maritime Fluoride-salt-cooled High-temperature Reactor (FHR) are transferred to a larger terrestrial FHR for continued utilization. Neutronic behavior is analyzed using a high-fidelity Monte Carlo framework: the Hyper-Fidelity (HxF) tool models detailed depletion in the maritime reactor, while the Search Equilibrium tool determines the equilibrium steady-state fuel composition in the terrestrial core. Results indicate that the hybrid approach significantly enhances total energy extraction per unit mass of heavy metal compared to independent single-reactor operation. While a conventional once-through cycle achieves an average burnup of 148 MWd/kgHM, transferring pebbles at burnup of 47.5 MWd/kgHM enables a subsequent burnup of 110 MWd/kgHM in the terrestrial core, yielding a total of 157.5 MWd/kgHM, a 6.4% increase. Additionally, performance improves further at lower transfer burnups, with 35 MWd/kgHM transfers achieving total burnups up to 163 MWd/kgHM. These results demonstrate that sequential burning of pebbles in spectrally different reactor environments can outperform the energy extraction limit of single-core operation, providing a potential path toward improved fuel utilization and reduced waste generation for advanced FHR fleets, and potentially other TRISO fueled reactors.

Speaker: Josef A. H. Hisanawi (Department of Physics, University of Oslo)

18:10 Nuclear excitation functions for medical radionuclide production: targeted radionuclide therapy via natIr(d,x)193mPt

Radionuclides that decay with Meitner-Auger electrons are believed to have potential in targeted radionuclide therapy, due to their short ranges on the scale of the cellular nucleus with high precision dose delivery. To establish production routes, accurate nuclear data for optimization of irradiation and yield predictions are required. The Meitner-Auger emitter $^{193m}$Pt is of interest due to its therapeutic potential particularly labelled to the chemotherapeutic drug cisplatin, which may streamline treatment and also avoid chemical toxicity.

A stacked target irradiation was performed at Lawrence Berkeley National Laboratory’s 88-Inch Cyclotron. The stack included 10 foils of iridium, with monitor foils of nickel, copper and iron placed within each compartment. The stack was irradiated with a 33 MeV deuteron beam, and the beam was completely degraded in the stack, yielding cross section measurements from threshold to 33 MeV. The beam current through the stack was determined using recommended monitor reactions, and energy assignments were obtained through Anderson-Ziegler stopping power simulations. Following end-of-irradiation, gamma-ray spectroscopy was performed to quantify the activities for all observed radionuclides.

This work yielded cross sections for 42 channels of deuteron induced reactions on natural iridium, copper, nickel and iron from threshold to 33 MeV, as well as thick target yields of the measured channels of iridium. I will present the key results of the final cross sections from the iridium targets and monitor foils, and the optimum deuteron energy window to maximize the production and radiopurity of $^{193m}$Pt via this reaction

Speaker: Hannah Ekeberg (University of Oslo)

18:10 Probing the Nuclear Shape of Triple Point E(5) Symmetry Candidate 140Sm

In this gamma spectroscopy analysis, we aim to measure the spectroscopic quadrupole moments of excited states and electromagnetic transition rates in neutron-deficient 140Sm. The experimental data was collected during a Coulomb excitation experiment at ISOLDE in 2017, utilizing a 140Sm beam on a 208Pb target and the Miniball HPGe array alongside a CD particle detector.

The chain of samarium isotopes exhibits a diverse range of nuclear shapes, from spherical at the N=82 shell closure to well-deformed for both the neutron-rich isotopes beyond A=154 and the very neutron-deficient ones below A=134. The nucleus 152Sm is a well-known example for so-called X(5) symmetry at the transition from spherical vibrational to deformed rotational behavior. The case of 140Sm, on the other hand, is a candidate for a nucleus with E(5) symmetry, corresponding to the triple point in the phase diagram for shape phase transitions between spherical, oblate, and prolate shapes. This makes electromagnetic matrix elements in 140Sm sensitive benchmarks for theoretical nuclear structure models. We will present preliminary results from our analysis during the workshop.

Speaker: Gulla Torvund (University of Oslo)

18:10 Scalability of Heat-Pipe cooled Reactors for Remote and Autonomous Applications

Heat-Pipe cooled Reactors (HPRs), which were originally intended for space applications, are of particular interest for remote/autonomous operations as their designs are simple, compact, and transportable. Historically most HPR designs produce only limited thermal power in the kilowatt range and/or utilize highly enriched fuel. This work investigated how reactor design principles can be used to scale up HPRs to higher nominal powers while using less-enriched fuel and without exceeding material limits. The effective core height, number of fuel assemblies, and heat-pipe parameters were used to constrain the design parameter of the final HPR core. The open-source particle transport code OpenMC was used to determine the average volumetric heat rate of a fuel pin, which was coupled with an iterative finite-difference scheme to determine local temperature distributions in the reactor core. These were used to set new material temperatures in the neutronics model, and the process was repeated until the neutron multiplication factor had converged within a tolerance of 50 pcm. The design was simulated at thermal power levels between 5 and 20 MWth, and peak material temperatures were calculated and compared.

Speaker: Baltasar Johannes Hemmerle (Department of Oslo, University of Oslo)

18:10 Sensitivity of Fission Yield Predictions to Nuclear Level Density and Gamma Strength Function Models in Reactor Applications

Reliable fission yield data are essential input for reactor depletion simulations, decay heat predictions, and fuel cycle assessments. The high accuracy of these data is particularly important for decommissioning-related analyzes involving the characterization and subsequent handling procedures of irradiated materials. The statistical description of fission fragment de-excitation is based heavily on nuclear level densities and gamma strength functions, making these quantities key contributors to nuclear data-driven uncertainties in fission yield evaluations.

This contribution examines the accuracy and applicability of simulated results from reactor models operating with both thermal and fast neutron spectra. Emphasis must then be placed on the sensitivity of fission yield predictions to commonly used parameterizations of nuclear level densities and gamma strength functions within statistical reaction frameworks. The influence of nuclear structure inputs on fission fragment de-excitation pathways, and consequently on predicted isotopic inventories and activation levels, thus needs to be evaluated.

The aim is to clarify the connection between nuclear structure uncertainties and applied reactor observables, to compare uncertainty propagation in thermal and fast systems, and to motivate further cross-disciplinary efforts in nuclear data uncertainty quantification.

Speaker: Maia Wirgenes (University of Oslo and the Institute of Energy Technology)

18:10 Systematic comparison of experimental photon strength function extracted using the Oslo method to theoretical calculations

The Photon Strength Function (PSF) database hosted by the IAEA [1,2] provides both experimental data and theoretical calculations. Experimental PSF data extracted using the Oslo method were compared to two theoretical models recommended on the IAEA database website. One model is purely phenomenological (SMLO) while the other is based on microscopic calculations (D1M-QRPA).

For all the nuclei present in the database for which the Oslo method was used to extract the PSF, data were averaged over 1 MeV energy bins from 1 to 8 MeV and comparisons between experimental data and theoretical calculations were made as a function of the number of nucleons, protons or neutrons, and quadrupole deformation. The overall agreement is within an order of magnitude but systematic trends revealed both the presence of experimental outliers suggesting potential issues with some measurements, and global trends suggesting an incomplete theoretical description.
Oslo data were assigned quality indicators based on the quality of the uncertainty analysis performed as well as the availability of external nuclear data used for normalization. Outliers were identified and correlations as function of the nuclear mass and quadrupole deformation will be presented.

This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contracts No. DE-AC02-05CH11231 and by the US Nuclear Data Program.

[1] https://www-nds.iaea.org/PSFdatabase
[2] S. Goriely, P. Dimitriou, M. Wiedeking et al., The European Physical Journal A 55, 172 (2019), 10.1140/epja/i2019-12840-1

Speakers: Dr Kgashane Malatji (University of California Berkeley), Thibault Laplace (University of California, Berkeley)

18:10 Systematic Studies of Molybdenum Level Densities

The overall goal of nuclear astrophysics is to understand the creation of the elements in the universe and the nucleosynthesis processes that are involved. Nuclear Level Densities (NLD) are used as inputs to calculate reaction rates for nuclear reactions that occur in different stellar environments. NLDs represent the number of excited energy levels present in a nucleus at a specific excitation energy and are challenging to constrain experimentally. Systematic studies of NLDs allows us to examine trends across isotopic chains to develop predictive models for nuclei farther from stability. In this work, the molybdenum isotopic chain was chosen due to the amount of nuclear data available on the NLD and its relevance for astrophysics and applications. TALYS was used to obtain calculations for the NLDs (both phenomenological and microscopic models) for the 93Mo - 110Mo isotopes. Bayesian Analysis was then performed using the available NLD models along with the existing experimental NLD data from the Oslo Method. The experimental data and the theoretical models were compared against each other to identify the trends across the isotopic chain. To provide model-independent NLD constraints for the stable Mo isotopes for our systematic studies, experiments were conducted to measure the NLD for 93Mo and 94Mo using (p,n) and (d,n) reactions on a 93Nb target. Experiments were performed at the Edwards Accelerator Lab at Ohio University using the Time-of-Flight tunnel and the Beam Swinger facility and data are currently under analysis using the Particle Evaporation Method.
In this presentation, I will provide an overview of systematic NLD trends in the Mo isotopic chain and will describe the recent results obtained via the Particle Evaporation Method.

Acknowledgement: This work was supported by the Office of Defense Nuclear Nonproliferation Research and Development within the U.S. Department of Energy’s National Nuclear Security Administration.

References: 
[1] Koning, A., Hilaire, S., and Goriely, S., (2023) Eur. Phys. J. A 59, 131 
[2] Chankova, R. et al. (2006) Phys. Rev. C, 73, 034311.
[3] Schiller, A. et al. (2003) Phys. Rev. C, 68, 054326.

Speaker: Amadie Wijenarayana (Ohio University)

18:10 The Historical Economics of the US Nuclear Fleet

Between the 1960s and early 1980s, the United States undertook the world’s largest nuclear power construction program. Early projects benefited from declining construction costs, making nuclear power economically competitive with fossil alternatives. From the early 1970s and onward, however, overnight construction costs (OCC) escalated rapidly, coinciding with regulatory tightening, high inflation and interest rates, and increasing project size and complexity. This cost escalation ultimately ended the U.S. nuclear build-out and has since been extensively studied. Most existing analyses focus on construction costs alone, leaving unresolved the question of whether nuclear investments were economically successful over their full operating lifetimes.
This paper addresses that gap by evaluating the historical economics of the U.S. nuclear fleet using lifetime performance metrics rather than construction costs alone. By combining reactor-specific OCC data with detailed operational, fuel, and financial data, the study reconstructs Levelized Cost of Electricity (LCOE) for U.S. nuclear reactors over their initial operating lifetimes.

Fuel costs are estimated using a physics-based model of the uranium fuel cycle calibrated to historical reported fuel cost reporting, while O&M costs are reconstructed using plant-specific data supplemented by fleet-level benchmarks.
The results contribute a long-missing perspective to nuclear cost studies by evaluating whether the U.S. nuclear build-out was economically successful when judged on realized lifetime performance rather than construction outcomes alone. The findings offer empirical insights for current nuclear investment debates, particularly regarding optimal reactor size, project complexity, and the economic lessons relevant for future nuclear deployment.

Speaker: Vala Valsdottir (University of Oslo)

Tuesday 19 May

08:30 → 09:00 Coffee

09:00 → 11:00 Breakfast session

Convener: Artemis Spyrou

09:00 Determining the electric or magnetic nature of the low-energy enhancement in nuclei

The photon strength function (γSF) defines the likelihood of photon emission as a function of photon energy and the properties of the initial and final nuclear states. Of the features present in the γSF, an enhancement in the low-energy region has been observed in some nuclei. Despite two decades of research, the electromagnetic nature of this enhancement remains an open question. This low energy enhancement in the γSF significantly impacts our understanding of how elements are created in stars and how the nucleus is structured. In this work, we present the results from an experiment on the γSF of $^{70}$Zn. High-energy states in $^{70}$Zn were populated from the decay of $^{70}$Cu produced, separated and delivered to an experimental station in two different $\beta$-decaying states, the 6$^{-}$ ground state and 1$^{+}$ isomeric state at 243-keV. The results show conclusively for the first time that the enhancement in the γSF of this nucleus is of magnetic nature. This insight answers a long-open question about atomic nuclei and directly impacts our predictive capabilities in nuclear science.

Speaker: Sean Liddick (FRIB/MSU)

SNL_Oslo26_M1.pdf

SNL_Oslo26_M1.pptx

SNL_Oslo26_M1.pptx

09:30 Photon Strength Function of $^{90}$Zr from radiative $^{89}$Y(p,$\gamma$) using GRETINA

The electromagnetic dipole response of atomic nuclei is fundamental for understanding nuclear structure and reaction dynamics. Measurements of photon strength functions (PSFs) have revealed phenomena such as Low-Energy Enhancement, significantly affecting astrophysical reaction rates relevant to nucleosynthesis.

To investigate the shape of the PSF and the observed excitation modes below S$_{n}$, the sub-barrier $^{89}$Y(p,$\gamma$)$^{90}$Zr radiative capture reaction was performed at four (4) incident proton beam energies. The resulting $\gamma$ decays were measured using Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) [1]. By applying the Shape Method [2], the shape of the PSF will be extracted for $\gamma$-ray energies below S$_{n}$. This analysis aims to provide new constraints on the shape of PSF in $^{90}$Zr and to shed light on the LEE's underlying physical mechanisms at the lowest accessible energies.

In this talk, preliminary results on the shape of $^{90}$Zr PSF obtained from radiative proton capture using the Shape Method will be discussed.

[1] S. Paschalis, I.Y. Lee, A.O. Macchiavelli et al., Nucl. Instrum. Methods A 709, 44 (2013).
[2] M. Wiedeking, M. Guttormsen, A.C. Larsen et al., Phys. Rev. C 104, 014311 (2021).

Research supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contracts No. DE-AC02-05CH11231 and by the US Nuclear Data Program.

Speaker: Dr Kgashane Malatji (University of California Berkeley)

OWS2026.pdf

10:20 Neutron-capture cross sections for heavy-mass fission fragments constrained with the $\beta$-Oslo method

The upcoming operation of the nuCARIBU facility at ATLAS will enable new measurements of neutron rich La isotopes, which are important both for U.S. stockpile stewardship applications and for understanding the nucleosynthesis of heavy elements in the cosmos. In particular, constraining the $ ^{146} $La(n,$ \gamma $)$ ^{147} $La and $ ^{147} $La(n,$ \gamma $)$ ^{148} $La reactions through experimentally determined nuclear level densities (NLDs) and $\gamma$-ray strength functions ($\gamma$SFs) will improve neutron reaction network calculations in the $ A = 147 $ mass region under neutron rich conditions.

These nuclei lie in a structurally interesting region of the chart of nuclides, between Mo and Nd, where isotopic chains have exhibited distinct trends in their low energy enhancement (LEE) of the $ \gamma $SF. For Mo and Nd isotopes, the LEE decreases with increasing neutron number. In contrast, measurements of Sn isotopes show no clear evidence of an LEE, a behavior also observed in $ ^{140} $Ba in an Oslo style experiment at CARIBU at ATLAS. For La, Oslo style measurements of $ ^{138,139,140} $La at the Oslo Cyclotron Laboratory indicate either a modest LEE or a plateau like behavior at low $ \gamma $ ray energies.

To extend these systematics further from stability, preparations are underway for an experiment that will use the $ \beta $ decay of $ ^{147,148} $Ba beams to populate excited states in $ ^{147,148} $La. The resulting $ \gamma $ rays at high excitation energies will be studied via total absorption spectroscopy with the Summing NaI (SuN) detector and the SuN Tape system for Active Nuclei (SuNTAN). I will present the experimental concept for this upcoming campaign at nuCARIBU, planned for the second half of this year, and discuss anticipated challenges specific to this region, eight neutrons away from stability.

Speaker: Adriana Sweet (Lawrence Livermore National Laboratory)

sweet_Oslo2026.pdf

sweet_Oslo2026.pptx

10:40 Constraining the $^{95}$Zr(n,$\gamma$) cross section using SONIC at Horus

The $^{95}$Zr(n,$\gamma$) cross section is crucial for understanding the intermediate neutron capture process (i process), as it directly affects the production and abundance of Molybdenum isotopes. The observed Molybdenum overabundance in presolar grains represents one of the most significant signatures of i-process nucleosynthesis. At the same time, $^{95}$Zr remains a branching point in the slow neutron capture process (s process), where its long-lived nature allows β-decay to compete with the formation of $^{96}$Zr.
Because $^{95}$Zr is unstable, a direct measurement of its neutron capture cross section is currently not feasible. Using the Oslo method, we have experimentally constrained the $^{95}$Zr(n,γ) cross section for the first time. The $^{96}$Zr(p,p’) reaction was studied at the 10 MV FN-Tandem accelerator at the Institute for Nuclear Physics, University of Cologne, employing the SONIC@HORUS detector array. By applying the newly developed “Shape” method, we significantly reduced model uncertainties. We present preliminary results and discuss their implications for i-process nucleosynthesis, with reference to the s process.

Speaker: Dennis Muecher (Institute for Nuclear Physics, University of Cologne)

Oslo Workhop 2026 Dennis.pdf

Oslo Workhop 2026 Dennis.pptx

11:00 → 11:30 Coffee

11:30 → 13:00 Midday Session

Convener: Andrea Richard

11:30 Systematic studies of nuclear level densities from particle evaporation technique

In this work, new results from a series of particle-evaporation experiments on nuclei spanning a wide mass range, including the fission-product region, are presented. The measurements include energy spectra of emitted neutrons and charged particles obtained over a range of excitation energies.
The experimental data are compared with statistical-model calculations performed with commonly used reaction codes. A detailed assessment of model performance is provided, with particular emphasis on the sensitivity to the choice of level-density models. Systematic trends in the extracted level-density parameters across different nuclei are discussed, highlighting regions where current models reproduce the data well and where significant deviations remain.
These results provide new benchmarks for improving reaction modeling and offer insight into one of the most important nuclear parameters—the nuclear level density. The identified systematics contribute to a more reliable description of compound-nucleus reactions and are relevant for applications in nuclear astrophysics, reactor physics, and nuclear data evaluations.

Speaker: Alexander Voinov (Ohio University)

Presentation_Voinov_1.pdf

Presentation_Voinov_1.pptx

12:00 Nuclear strength functions from microscopic models

Understanding the structure of heavy and neutron-rich nuclei is essential for the rapid neutron-capture process (r-process). The simulation of this process, which synthesizes half of the elements heavier than iron, relies on accurate predictions of nuclear masses and reaction rates (neutron capture, photo absorption, beta decay, etc.) for thousands of neutron-rich nuclei. However, since experimental data are scarce in this exotic region of the nuclear chart, theoretical models are crucial to bridge this gap.

Models based on nuclear energy density functionals (EDFs) represent our current best hope to provide this plethora of data. Such an approach describes a nucleus in terms of its constituent nucleons while the equations remain sufficiently tractable for global application. We are building a new class of EDF-based models aimed at providing all necessary data to astrophysical applications: the Brussels-Skyrme-on-a-Grid or BSkG-series [1-6]. Exploiting the concept of spontaneous symmetry breaking to the utmost, the BSkG models accord the nucleus an extreme amount of freedom: nuclear shapes range from spheres and axially symmetric ellipsoids but also exhibit triaxial deformation, reflection asymmetry, non-zero angular momentum or all of these combined! Global tabulations of accurate predictions of these models are available for (i) nuclear ground-state quantities like masses, radii and deformation, (ii) more involved quantities including fission properties [7] and (iii) nuclear level densities (NLD), which are in excellent agreement with Oslo data where available [8].

Our next big goal is the prediction of photon strength functions (PSF) across the entire nuclear chart through quasi-particle random phase approximation (QRPA) calculations. This way, we will complete the nuclear data required to predict consistently electromagnetic reactions rates from a single nuclear-structure model, thereby making r-process simulations more robust to nuclear input. This project is also of interest to nuclear structure: extending our symmetry-broken solver to QRPA calculations will allow us to study the effect of exotic deformation modes, e.g. triaxial, octupole, …, on nuclear PSFs.

In this talk, I will start by discussing the BSkG series of models and discuss some key points on how spontaneous symmetry breaking helps us improve our global description of the properties of nuclei, and in particular our predictions of nuclear level densities [8]. Then, I will highlight some of the recent achievements made in the construction of our symmetry-broken QRPA solver and show the first BSkG predictions of PSFs for triaxially-deformed systems.

[1] G. Scamps et al., EPJA 57, 333 (2021).
[2] W. Ryssens et al., EPJA 58, 246(2022).
[3] G. Grams et al., EPJA 59, 270 (2023).
[4] W. Ryssens et al., EPJA 59, 96 (2023).
[5] G. Grams et al., EPJA 61, 35 (2025).
[6] G. Grams et al., arXiv:2601.05968 (2026).
[7] A. Sánchez-Fernández, PLB 874, 140287 (2026).
[8] S. Goriely et al. PRC 113, 014320 (2026).

Speaker: Pepijn Demol (Université Libre de Bruxelles)

Oslo_BSkG.pdf

12:20 The electric dipole response of nuclei with Z<50

This study aims at understanding the dependence of the E1 strength in the transition region from vibrational to rotational nuclei. Below the Z = 50 closed shell Sn nuclei, week deformations start to build in. In the case of 106Pd, the observed band structures were reported to correspond to a quadrupole deformation of β2 = 0.175 [1], where calculations within the tilted-axis cranking model [2] were presented. The low-lying E1 states in the transitional Pd nuclei are expected to be weak and strongly fragmented. The chosen method of study is the Nuclear Resonance Fluorescence(NRF) [3] method, a two-step photonuclear process which consists of the absorption of a photonand the subsequent resonant re-emission of gamma rays.

An NRF experiment was conducted at TU Darmstadt, using the DHIPS (Darmstadt High-Intensity Photon Source) setup. A monoenergetic electron beam, with a current of 40 μA, impinging on two Ag bremsstargets (1mm and 5 mm thickness) and creating bremsstrahlung radiation was employed. The endpoint energy was situated at 8.7 MeV. An array of three high-purity Germanium (HPGe) detectors, positioned at 130◦ and two at 90◦ with respect to the incoming beam, was employed. They were equipped with bismuth germanate (BGO) shields for active Compton suppression and additionally mounted in lead collimators. The primary target consists of 0.991 g of
106Pd and was placed in between the three detectors.

This first measurement on 106Pd uncovered new transitions in the 3.5-8 MeV energy range. The data is currently being analyzed and will provide an overview of the γ-ray transition energies, integrated cross-sections and reduced transition strengths.

References:
[1] C.E. He et al., Phys. Rev. C 86, 047302 (2012);
[2] S. Frauendorf, Nucl. Phys. 557, 259c (1993);
[3] L.I. Schiff, Phys. Rev. 70, 761-762 (1946).

*This work is supported by Project ELI-RO/DFG/2025_013 IATP-NP 2.0 funded by the Institute of Atomic Physics, Romania and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 499256822 – GRK 2891 “Nuclear Photonics”.

Speaker: Teodora Sebe

Oslo_Worksho_Sebe.pdf

Oslo_Worksho_Sebe.pdf

Oslo_Worksho_Sebe.pptx

12:40 The Total Relativistic Coulomb Excitation Cross Section of Neutron-Rich Tin Isotopes and Implications on Energy-Density Functionals

Exploring the equation of state (EoS) of isospin-asymmetric nuclear matter is essential for understanding the structure of exotic nuclei and processes in neutron-rich astrophysical environments. The symmetry energy, which encodes the isospin dependence of the EoS, is commonly characterized by its value at saturation $J$ and its slope $L$, the latter of which remains poorly constrained. In this work, we investigate the sensitivity of the total Coulomb excitation cross sections ($\sigma_C$) of neutron-rich tin isotopes $^{124-132}$Sn to the parameterization of the symmetry energy around saturation density. At relativistic beam energies above 500 MeV$/$u, $\sigma_C$ is dominated by the excitation of the Isovector Giant Dipole Resonance (IVGDR). For medium-heavy and heavy neutron-rich nuclei, $\sigma_C$ exhibits a strong correlation with dipole polarizability $\alpha_D$, which is sensitive to the isovector properties of the nuclear EoS near and below saturation density [1,2].

Although extraction of $\sigma_C$ does not require reconstruction of the full excitation-energy spectrum, detector response effects depending on the kinetic energies of the center-of-mass neutrons remain relevant. In turn, the neutron kinetic-energy distributions depend on statistical decay properties governed by nuclear level densities. We present a comparative analysis of two R3B experiments employing LAND and NeuLAND [3] neutron detectors at different beam energies. For measurements performed at $\sim$500 MeV/u with LAND, limited neutron acceptance above $\approx$3 MeV (fragment rest frame) requires generating detector response matrices using statistical decay simulations [4]. In contrast, measurements with NeuLAND at higher beam energies achieve near-complete acceptance for evaporated neutrons, enabling a direct extraction of the total Coulomb excitation cross sections above the neutron separation threshold. This removes systematic uncertainties associated with statistical decay modeling.

The extracted $\sigma_C$ values from the two experimental data sets are compared with coupled channels calculations [5] employing B(E1) and B(E2) inputs from QRPA calculations with a set of 24 relativistic and non-relativistic energy density functionals (EDFs). All models overestimate the measured cross sections and fall outside the range of experimental uncertainties for $^{124}$Sn, $^{130}$Sn and $^{132}$Sn, including interactions with the lowest predicted values of $L$. These preliminary cross sections, pending a stricter experimental uncertainty assessment, are consistent with the findings of the $\alpha_D$ measurement of $^{124}$Sn carried out at the RCNP facility [6].

[1] Horvat, A., Ph.D. thesis, Technische Universität Darmstadt, Germany (2021).

[2] Roca-Maza, X., Paar, N., & Colò, G., J. Phys. G: Nucl. Part. Phys., 42, 034003 (2015).

[3] Boretzky, K. et al., Nucl. Instrum. Methods Phys. Res. A, 1014, 165701 (2021).

[4] Rossi, D. et al., Phys. Rev. Lett., 111, 242503 (2013).

[5] C. A. Bertulani, L. F. Canto, M. S. Hussein, and A. F. R. de Toledo Piza, Phys. Rev. C \textbf{53}, 334 (1996)

[6] Bassauer, S. et al., Phys. Lett. B, 810, 135804 (2022).

Speaker: Andrea Horvat (RBI Zagreb)

HorvatOslo052026.pdf

13:00 → 14:30 Lunch

14:30 → 16:10 Afternoon session

Convener: Stephane Goriely

14:30 Exploring the i process: Constraining the $^{87,88}$Kr(n,$\gamma$)$^{88,89}$Kr Reaction Rates via the $\beta$-Oslo Method

How elements beyond Fe are produced in stars continues to be an open question in nuclear astrophysics. Traditionally, two main pathways along the neutron-rich side of the chart of nuclides were shown to explain heavy element nucleosynthesis: the slow (s-) and rapid (r-) neutron capture processes. However, in recent astronomical observations, especially in Carbon-Enhanced Metal Poor (CEMP) stars, the abundance patterns of certain elements cannot be explained by these two processes alone. Hence, an additional, independent nucleosynthesis pathway is required to explain these observed abundances, being the intermediate (i-) neutron-capture process.
For nuclei that are involved along the i-process pathway, structural properties such as masses and $\beta$-decay half-lives are experimentally well constrained except for neutron-capture reaction rates, which are almost entirely provided by theory.

Recent sensitivity studies have shown that the Rb/Sr abundances are strongly affected following the neutron-capture reactions on Kr isotopes.
In this talk, the first experimental constraints on the $^{87,88}$Kr(n,$\gamma$) $^{88,89}$Kr reactions will be discussed utilizing the $\beta$-Oslo method. This experiment utilized the CARIBU facility at Argonne National Laboratory using the indirect method of $\beta$-decays from $^{88,89}$Br into $^{88,89}$Kr. Subsequent $\gamma$-rays were identified the using the Summing NaI(Tl) detector, SuN, and the SuNTAN tape transport system. This presentation will feature the recently published results of the experimentally constrained cross section for $^{88,89}$Kr, both obtained by exploiting their statistical properties. The impact of these reactions on the final abundances of Rb and Sr will be discussed in this talk.

Speaker: Sivahami Uthayakumaar (Michigan State University / FRIB)

15:00 Nuclear level densities extracted from $(d,p\gamma)$ reactions via fluctuation analysis

Nuclear level densities (NLDs) are fundamental for describing statistical properties of atomic nuclei and play a central role in nuclear structure and reaction studies as well as in nucleosynthesis calculations.
In this work, we present the determination of the NLDs for the even tin isotopes $^{116,118,120}$Sn. High-resolution nuclear spectra from $(d,p\gamma)$ reactions, measured with the SONIC@HORUS setup at the 10-MV FN Tandem accelerator at the University of Cologne, were analyzed using the fluctuation analysis technique. This approach enables a direct extraction of the densities for $1^{-}$ states without relying on assumptions about spin distributions and hence providing a model-independent determination of the underlying NLD. The experimental data are compared to theoretical models including spin distributions.

Speaker: Johann Isaak

isaak_oslo_final.pptx

15:30 Systematic Study of Nuclear Level Density Models for Unresolved Resonance Region Evaluations

In this work, we compare the performance of three well-known phenomenological nuclear level density models for cross-section evaluations in the unresolved resonance region. Phenomenological model parameters are optimized by using least-squares analysis to simultaneously fit level density, cross-section, neutron strength, and capture width data from the EXFOR and ENSDF databases. Calculations are accomplished using the Hauser-Feshbach model and a novel implementation of the Back-Shifted Fermi Gas Model, Gilbert-Cameron Composite Model, and Generalized Superfluid Model in the cross-section evaluation code SAMMY. We evaluate model performance by examining both the goodness of fit to experimental data and the propagation of model differences to shielding and critical benchmark simulations. Based on agreement with experimental benchmark results, recommendations are made to evaluators on level density model choice.

Speaker: Justin Loring (University of Tennessee Knoxville)

Level Density Conference Presentation Version 2-3.pdf

Level Density Conference Presentation Version 2-3.pptx

15:50 Statistical properties of $^{133}$Xe and the $^{132}Xe(n,$\gamma$) cross section

In this talk we present the extracted nuclear level density, and $\gamma$-strength function for $^{133}$Xe using the inverse-Oslo method. These are the first statistical properties extracted below 6 MeV for any xenon isotope. The experiment was performed in inverse-kinematics at iThemba LABS with an annular particle telescope and a scintillator array consisting of LaBr$_3$ and BGO-shielded HPGe Clover detectors. Shell-model calculations of the statistical properties of $^{133}$Xe were done to explore the $\gamma$-strength function, along with the parity dependence of the nuclear level density. With these experimentally constrained statistical properties with inverse-Oslo, we constrain the (n,$\gamma$) cross section on $^{132}$Xe with TALYS and compare it with previous measurements.

Speaker: Hannah Berg

OWS_Xe133_HCBerg.pdf

OWS_Xe133_HCBerg.pptx

16:10 → 16:30 Coffee

16:30 → 18:30 Discussion session: Level Density

Convener: Peter von Neumann-Cosel (Institut für Kernphysik, Technische Universität Darmstadt)

Oslo2026_gsf_discussion.pdf

Oslo2026_gsf_discussion.pptx

Wednesday 20 May

08:30 → 09:00 Coffee

09:00 → 11:00 Breakfast session

Convener: Johann Isaak

09:00 Exploring PDR and IV-GQR Strengths with Inelastic Proton Scattering at the Krakow Cyclotron Centre Bronowice

The experimental campaign carried out at the Krakow Cyclotron Centre Bronowice, aimed at determining the strength of the Pygmy Dipole Resonance (PDR) and the isoscalar Giant Quadrupole Resonance (IS-GQR), will be presented. Both studies were performed using the same experimental setup and based on inelastic proton scattering techniques. A series of measurements focusing on the PDR in stable nickel isotopes was conducted to investigate the evolution of the PDR strength as a function of the N/Z ratio along the isotopic chain. In addition, an experiment dedicated to the measurement of the IS-GQR in 120Sn was carried out. Preliminary results from both experiments will be presented and discussed.

Speaker: Agnese Giaz (INFN - Sezione di Milano)

GIAZ_Oslo.pptx

09:30 Configuration Interaction Shell Model Studies of Photon Strength Functions

In this contribution, I will report on recent CI-SM results covering the large-scale evaluation of electric dipole PSF in light and mid-mass nuclei, their applications, as well as first calculations of isoscalar and isovector modes in neutron-rich nuclei, permitting a CI-SM insight into the isospin-mixing of the PDR. If time allows, I will also discuss recent progress of establishing an effective computation scheme within the PGCM method to obtain the magnetic dipole transition strengths.

Speaker: Kamila SIEJA

oslo26_ks.pdf

10:00 Exploring the Pygmy Dipole Resonance across the Sn mass region with the Oslo method

The pygmy dipole resonance (PDR) is commonly associated with an excess $E1$ strength on top of the low-energy tail of the giant dipole resonance (GDR) close to the neutron-separation energy in stable and unstable heavy nuclei. While its detailed structure, properties, and origin remain a matter of ongoing debates and research, the neutron-skin oscillation picture of this feature still prevails and suggests some dependence of the PDR strength on neutron excess. This might have further consequences for neutron-capture rates relevant for heavy-element nucleosynthesis [1], making a systematic investigation of the PDR and the low-lying $E1$ strength in general in different isotopic chains particularly interesting from the nuclear structure and astrophysical perspectives.

This work presents the most recent update on a consistent systematic study of the low-lying electric dipole strength and the potential PDR in stable and unstable Pd, Cd, In, Sn, and Sb isotopes with the Oslo method [2].The analysis focuses on dipole $\gamma$-ray strength functions (GSF) below the neutron threshold extracted from particle-$\gamma$ coincidence data from light-ion induced reactions studied at the Oslo Cyclotron Laboratory (OCL). The most recent ($p,p^{\prime}\gamma$) and ($\alpha,p\gamma$) experiments have been performed with a new array of 30 LaBr3(Ce) scintillator detectors (OSCAR) with an improved energy resolution and timing properties for the selection of particle-$\gamma$ events as compared to the earlier experiments done with the NaI(Tl) detector array CACTUS. All previously published GSFs of $^{105, 107, 111, 112}$Cd [3] and $^{105-108}$Pd [4] isotopes have been re-analysed to provide a more consistent analysis of the strengths in the Sn mass region.

With a wide span of isotopes (from unstable, neutron-deficient $^{109}$In to unstable, neutron-rich $^{127}$Sb), these dipole strengths provide an excellent case for investigation of the PDR evolution with increasing proton-neutron asymmetry, comparing it with different theoretical approaches, and revealing a possible impact of this feature on the astrophysical radiative neutron-capture processes. Combining these data with available $(\gamma,n$) cross sections and the $E1$ and $M1$ strengths from relativistic Coulomb excitation experiments allows us to extract the low-lying $E1$ component from the total dipole strength in each case. It was found to exhaust $\approx 1-3\%$ of the classical Thomas-Reiche-Kuhn (TRK) sum rule, being nearly constant throughout the whole chain of Sn isotopes and weakly increasing with neutron number in Cd and Pd isotopes. This finding is in contradiction with the majority of theoretical approaches, such as, e.g., relativistic quasi-particle random-phase and time-blocking approximations, predicting a strong, steady increase in the low-lying $E1$ strength with neutron number. Moreover, a presumably isovector component of the PDR was extracted for $^{118-122,124}$Sn. The most neutron-deficient case $^{109}$In studied recently at the OCL, on the contrary, exhibits little to no excess $E1$ strength below the neutron threshold, thus standing out among the neighbouring Cd and Sn isotopes.

Speaker: Maria Markova (University of Oslo)

Maria_Markova_presentasjon_ext.pdf

10:20 Threshold-aligned Pygmy Dipole Strength and Its Impact on Astrophysical (n, gamma) and (gamma, n) Rates

Accurate neutron-capture and photodisintegration reaction rates within the Hauser-Feshbach statistical framework are strongly governed by the nuclear $\gamma$-ray strength function and the nuclear level density. Uncertainties in these key nuclear inputs propagate directly into Maxwellian-averaged cross sections and constitute one of the dominant sources of uncertainty in modeling the astrophysical $r$-process. In this work, we examine the role of low-lying pygmy dipole strength in electric dipole transitions and assess its impact on $(n,\gamma)$ and $(\gamma,n)$ reaction rates in neutron-rich nuclei. The $\gamma$-ray strength functions are computed using a fully self-consistent relativistic quasiparticle random-phase approximation based on the DD-PCX energy density functional. These microscopic strength functions are then employed as input to Hauser-Feshbach calculations of astrophysical reaction rates. Our results demonstrate that enhancements in reaction rates are primarily dictated by the energetic alignment of the pygmy dipole strength with the neutron separation threshold, rather than solely by the total amount of low-energy dipole strength. When the pygmy mode is located close to the neutron threshold, both neutron-capture and photodisintegration reaction rates can be significantly enhanced. Pronounced rate enhancements are observed in nuclei such as $^{68}$Ni and $^{132}$Sn, where this alignment occurs. While thermal averaging moderates large local cross-section enhancements, the resulting rate increases remain astrophysically significant. For photodisintegration reactions, pygmy dipole effects become particularly important in very neutron-rich nuclei with low neutron separation energies, again leading to notable modifications when dipole strength and threshold energies coincide. These findings highlight the essential role of a realistic microscopic description of low-energy dipole strength near the neutron threshold for reliable $r$-process modeling and underscore the importance of close synergy between theoretical developments and experimental investigations of dipole response in neutron-rich nuclei.

Speaker: Dr Tanmoy Ghosh (Dept. of Physics, Faculty of Science, University of Zagreb)

Oslo_2026_Tanmoy_Ghosh.pdf

10:40 Study of the K quantum number of pygmy states in $^{154}$Sm

This work investigates the Pygmy Dipole Resonance (PDR) in the deformed $^{154}\mathrm{Sm}$ nucleus. The aim is to determine whether the PDR splits with respect to the K quantum number in a deformed nucleus, as is the case for the GDR. The study uses the $(\vec{\gamma},\vec{\gamma^\prime})$ reaction to excite dipole states at energies ranging from 3.5 MeV to 7.05 MeV, approaching the neutron separation energy at 8 MeV. Measurements were taken with the Clover Array at the HI$\gamma$S facility of the Triangle Universities Nuclear Laboratory. The facility’s polarised photon beam enables measurements using the asymmetry method to distinguish between 1−and 1+ states. Given that the first excited state of $^{154}\mathrm{Sm}$ lies only 82 keV above the ground state, the high-resolution beam mode (with an achievable energy spread below 2%) allows for the determination of decay branching ratios to the first 2+ state. These branching ratios are compared with the Alaga rules to predict the geometrical decay pattern. Additionally, the results are compared with the statistical decay model to ascertain whether the PDR decays predominantly statistically or geometrically. Although a study on $^{150}\mathrm{Nd}$ reported no K-splitting [1], the current study extends this investigation to the case of $^{154}\mathrm{Sm}$.

[1] O. Papst et al., Phys. Rev. Lett., 135 (2025) 052501.

Speaker: Refilwe Molaeng (School of Physics, University of the Witwatersrand)

11:00 → 11:30 Coffee

11:30 → 13:00 Midday Session

Convener: Sean Liddick (FRIB/MSU)

11:30 Experimental (d,p$\gamma$) Studies on the Kr and Sr Isotopes at the TRIUMF Facility

Neutron-capture cross sections play a vital role in our understanding of heavy element nucleosynthesis and applications relevant to nuclear security. Reaction networks in these regions involve short-lived isotopes for which capture cross sections cannot be measured via direct techniques. Instead reactions in these regions rely on calculations that can have uncertainties up to a few orders of magnitude. The Kr-Sr region is of particular importance for astrophysical processes and applications. In this presentation, I will discuss experimental (d,p$\gamma$) studies on the Kr and Sr isotopes at the TRIUMF Facility using the TIGRESS and SHARC arrays, and how measured particle-gamma coincidences can be used to provide experimental constraints for capture cross sections on short-lived nuclei using multiple techniques.

Speaker: Andrea Richard

12:00 The measurement of the reaction rate on 59Fe(n,g)60Fe and its astrophysical implication

60Fe, with its half-life of 2.6 My, is a great indicative isotope for recording the violent events in the cosmos. By measuring its abundances in the deep-sea sediment, lunar soil and the gammy-ray in space, scientists identified two accretion events (1.5–3.2) My and (6.5–8.7) My ago. These two events can be varying scenarios in the universe, like He- and C-burning shells inside massive stars, core-collapse supernovae, supernova shock running through the carbon and helium shells, electron-capture supernovae, SAGB stars and Type Ia supernova. No matter which scenario the it happens, 60Fe is only can be produced via the key nuclear reaction 59Fe(n,g)60Fe. Previous researches already indicated the rate plays significant role in the nucleosynthesis, however it is pretty difficult to measure this reaction directly as the neutron and 59Fe are both unstable.
In this talk, I will introduce the measurement of the reaction rate on 59Fe(n,g)60Fe. This experiment is performed on the Lanzhou Radioactive Ion Beam Line in China, the 60Mn beam is selected and delivered to the center of a BGO detector array named LAMBDA (LArge-scale Modular BGO Detection array). The LAMBDA covers about 85% of 4-pi solid angle and consists of 49 BGO crystal modules. By the measuring the total gamma ray of the beta decay from 60Mn to 60Fe, we can extract the nuclear level density and gamma strength function of 60Fe, then input them to the Hauser-Feshbach model to get the reaction rate on 59Fe(n,g)60Fe. This is so called beta-oslo method and firstly run in China. The uncertainty of reaction rate we get from this experiment is much less than the theoretical prediction, which lead us to better understand the formation of 60Fe in the universe.

Speaker: Prof. Shilun Jin (Institute of Modern Physics, Chinese Academy of Sciences)

12:20 Indirect experimental technique for constraining the $^{193,194}\mathrm{Ir}(n,\gamma)$ cross sections

Almost all elements heavier than iron are primarily produced through
the slow s- and rapid r- neutron-capture processes, which contribute about 50% each to the observed abundances [1]. The s-process, branching-point nuclei such as 192Ir play a crucial role, as neutron capture competes with β-decay affecting nucleosynthesis.
In this study, the $^{192}\mathrm{Ir}(n,\gamma)^{193}Ir$ and $^{193}\mathrm{Ir}(n,\gamma)^{194}\mathrm{Ir}$ reactions were investigated indirectly using data from the Oslo Cyclotron Laboratory. The $^{193,194}\mathrm{Ir}$ nuclei were populated via the $^{192}\mathrm{Os}(\alpha,t\gamma)$ and $^{192}\mathrm{Os}(\alpha,d\gamma)$ reactions. Due to the instability of 192Ir, its neutron-capture cross section cannot be measured directly. Instead, nuclear level densities and γ-ray strength functions were extracted using the Oslo Method [2] and used as input to the TALYS reaction code to calculate neutron-capture cross sections and Maxwellian-averaged cross sections (MACS). The $^{193}\mathrm{Ir}(n,\gamma)$ reaction results were compared to existing data for benchmark purposes [3].
The resulting $^{193}\mathrm{Ir}$ MACS values were implemented in the STAREVOL stellar evolution code [4] to assess their impact on the s-only isotope $^{192}\mathrm{Pt}$.
The results show that a reduced $^{192}\mathrm{Ir}(n,\gamma)$ reaction probability enhances β-decay branching, increasing the production of $^{192}\mathrm{Pt}$. Overall, the experimentally constrained data reduced the nuclear-physics uncertainty in the predicted $^{192}\mathrm{Pt}$ abundance by approximately 20%, providing improved
constraints for s-process nucleosynthesis models. In the workshop final
results of this study will be presented.

[1] Arnould, M., Goriely, S., and Takahashi, K. 2007.
[2] Schiller, A. et al. 2000.
[3] Zerkin, V. V., and Pritychenko, B. 2018
[4] L. Siess, E. Dufour, M. Forestini. 2000

This work is based on research supported in part by the National Re-
search Foundation of South Africa (Grant Number:PMDS22070734847),
SAINTS Prestigious Doctoral Scholarship, U.S. Department of Energy,
Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-
05CH11231 and the SARChI under grant No REP-SARC180529336567.

Speaker: Sebenzile Magagula (School of Physics, University of the Witwatersrand,)

2026_Magagula_Sebenzile_OSW.pdf

12:40 169-Tm(n, gamma) cross section and statistical gamma decay properties from DANCE measurements

Radiative neutron capture on rare-earth nuclei is important for applications ranging from nuclear astrophysics to reactor-related environments, yet experimental data remain limited, particularly for odd–odd systems. In our work [1], we present new results on the $^{169}$Tm$(n,\gamma)$ reaction, including an experimental determination of the capture cross section in the presence of considerable discrepancies in the unresolved-resonance region. Precise knowledge of the $^{169}$Tm$(n,\gamma)$ cross section in the keV region is essential for understanding the slow neutron-capture process in this mass region. In addition, we study the statistical $\gamma$ decay of the compound nucleus $^{170}$Tm, focusing on the scissors mode (SM) in the $M1$ photon strength function (PSF), for which data in odd–odd rare-earth nuclei are scarce.

The capture experiments were performed at the Los Alamos Neutron Science Center using the time-of-flight technique with the Detector for Advanced Neutron Capture Experiments (DANCE). DANCE provides high-efficiency detection of complete $\gamma$-ray cascades following neutron capture, enabling detailed studies of level density (LD) and PSFs. These quantities are also crucial both for efficiency determination and for Hauser–Feshbach cross-section calculations.

The capture cross section was determined from 1.8 eV to 0.97 MeV, representing the broadest neutron-energy range measured for this isotope. Eight new resonances were observed and their parameters extracted using SAMMY [2]. In the resolved-resonance region, the measured cross section agrees well with ENDF/B-VIII.0 [3], JEFF 3.3 [4], and JENDL-5 [5], while in the unresolved-resonance region it is generally lower than the evaluations.

The statistical $\gamma$ decay of $^{170}$Tm was investigated using coincident spectra constructed from individual resonances. These were compared with statistical simulations using the DICEBOX code [6] to test different LD and PSF models. Previously reported model parameters for odd–odd rare-earth nuclei [7, 8], as well as SMLO and D1M-QRPA PSF models from the Reference Database for Photon Strength Functions [9], fail to reproduce the measured spectra. The best agreement is obtained with the SM centered at 3.3 MeV, width of 1.0 MeV, and strength comparable to that observed in neighboring $^{168}$Er [10], combined with the MGLO [11] $E1$ PSF model; the Back-Shifted Fermi Gas LD model is favored.

Finally, the impact of the measured cross section on stellar nucleosynthesis was evaluated. The derived slow-process abundance of $^{169}$Tm is expected to increase by a factor of 1.26, while changes in the abundances of heavier nuclei remain at the level of approximately 0.2%.

[1] I. Knapova, K. Horcickova et al., Physical Review C 112 (2025) 014612.
[2] N. M. Larson, Updated User’s Guide for SAMMY: Multilevel R-Matrix Fits to Neutron Data Using Bayes’ Equations, Technical Report ORNL/TM-9179/R8, ENDF-364/R2, Oak Ridge National Laboratory, 2008.
[3] D. Brown et al., Nuclear Data Sheets 148 (2018) 1–142.
[4] A. J. M. Plompen et al., European Physical Journal A 56 (2020) 181.
[5] O. Iwamoto et al., Journal of Nuclear Science and Technology 60 (2023) 1–60.
[6] F. Becvar, Nuclear Instruments and Methods in Physics Research A 417 (1998) 434–449.
[7] J. Kroll et al., International Journal of Modern Physics E 20 (2011) 526–531.
[8] F. Pogliano et al., Physical Review C 107 (2023) 034605.
[9] S. Goriely et al., European Physical Journal A 55 (2019) 172.
[10] I. Knapova et al., Physical Review C 107 (2023) 044313.
[11] J. Kroll et al., Phys. Rev. C 88 (2013) 034317.

Speaker: Kamila Horčičková (Charles University)

Thulium_Oslo.pdf

13:00 → 14:30 Lunch break (Group photo)

14:30 → 16:00 Afternoon session

Convener: Stephane Hilaire (CEA, DAM, DIF)

14:30 Level densities and magnetic dipole strength functions of actinides in the shell-model Monte Carlo

Actinides are of great interest in astrophysics and in technology applications since
they can fission. However, the microscopic calculation of their statistical properties
presents a major theoretical challenge. The configuration-interaction (CI) shell-
model is a suitable framework to calculate these properties but the required model
spaces are much too large for conventional diagonalization methods. The shell-
model Monte Carlo (SMMC) method enables calculations in very large model spaces
and was applied to nuclei as heavy as the lanthanides [1]. Using the SMMC, we have
calculated level densities for the heaviest nuclei ever thus modeled, the actinides,
which require many-particle space dimensions as large as $10^{32}$ [2]. We find the
SMMC level densities to be in good agreement with Oslo method experiments,
neutron resonance data and level counting at low excitation energies.

We have also used the SMMC to calculate the magnetic dipole (M1) γ-ray strength
function (γSF) in a selected set of actinides [3]. We identify a low-energy enhance-
ment (LEE), the first such observation either theoretically or experimentally in
actinides. A LEE has been observed γSF of mid-mass nuclei, and conventional CI
shell model calculations suggest that this enhancement originates in the M1 γSF [4].
However, conventional CI shell model calculations are intractable in heavy nuclei,
and the standard approach to calculate γSFs – the quasiparticle random-phase ap-
proximation (QRPA) – does not reproduce the LEE. Using the SMMC, a LEE was
observed in chains of even-even [5, 6] and odd-mass [7] lanthanide isotopes.

We also observed in the M1 γSF of actinides a scissors mode that is built on top
of excited states. We compare our results with experiments by the Oslo group.

This work was supported in part by the U.S. DOE grant No. DE-SC0019521.

[1] For a recent review, see Y. Alhassid, in Emergent Phenomena in Atomic Nuclei
from Large-Scale Modeling: a Symmetry-Guided Perspective, edited by K. D.
Launey (World Scientific, Singapore, 2017), pp. 267-298.
[2] D. DeMartini and Y. Alhassid, arXiv:2509.26571.
[3] C. Rodgers, D. DeMartini and Y. Alhassid, arXiv:2511.11565.
[4] J. E. Mitdbø, A. C. Larsen, T. Renstrøm, F. L. Bello Garrote, and E. Lime,
Phys. Rev. C 98, 064321 (2018), and references therein.
[5] P. Fanto and Y. Alhassid, Phys. Rev. C 109, L031302 (2024).
[6] A. Mercenne, P. Fanto, W. Ryssens, and Y. Alhassid, Phys. Rev. C 110, 054313
(2024).
[7] D. DeMartini and Y. Alhassid, Phys. Rev. C 111, 034315 (2025).

Speaker: Dallas DeMartini (Yale University / Brookhaven National Laboratory)

14:50 Unravelling Photoabsorption in Light Nuclei: Insights from the PANDORA Project

The electric-dipole (E1) strength plays a central role in understanding photoabsorption reactions, offering insights into nuclear structure, collective excitations, and the nuclear response to external fields. While E1 strength has been extensively investigated in heavy nuclei (A > 90)—where shell effects and nucleon correlations are less pronounced—the situation is more complex for lighter nuclei (A < 60). In these systems, clustering phenomena, isospin mixing, nuclear deformation, and neutron–proton pairing strongly influence charged-particle branching ratios. As a result, the common assumption that the neutron-emission channel (g,xn) adequately represents the total photoabsorption cross section breaks down. This complexity not only challenges theoretical interpretation but also leads to divergent model predictions. The issue has direct consequences for astrophysics, particularly the study of ultra-high-energy cosmic rays (UHECRs). Since their origin and production sites remain unresolved, improving our knowledge of UHECR energy-loss processes during extragalactic propagation is important.

The PANDORA project (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) is an international effort dedicated to systematically measuring photoabsorption cross sections, as well as proton, alpha, and gamma branching ratios, for light stable nuclei (A < 60). These results will provide essential constraints for nuclear models, which in turn will be implemented in UHECR propagation simulations. In this presentation, I will introduce the goals of the PANDORA project and discuss preliminary findings on 12-13C from its first experiment.

Speaker: Luna Pellegri (University of the Witwatersrand)

2026-OsloWS-Pellegri.pptx

15:20 Investigating the Giant Dipole Resonance of $^{164}$Dy using Nuclear Resonance Fluorescence

The giant dipole resonance (GDR) represents one of the most fundamental nuclear excitations and dominates the photoresponse of virtually all nuclei. Its geometrical viewing is an isovector oscillation of the proton against the neutron body. This model also provides predictions for the $\gamma$-decay behavior of the GDR in elastic photon and $2^+_1$ Raman scattering reactions.

To rigorously test these for the first time, recently a photonuclear experiment was performed on the GDRs of the spherical and deformed nuclides $^{140}$Ce and $^{154}$Sm, respectively, at the High Intensity $\gamma$-ray Source (HI$\gamma$S) at TUNL, USA [1].
HI$\gamma$S's quasi-monochromatic, polarized, and tunable photon beam was employed to selectively photoexcite energy slices of the GDR and subsequently measure their $\gamma$-decay.
The results are in stunning agreement with the geometrical model predictions and provide new insights on the shapes of the nuclei, in particular the degree of triaxiality of the deformed $^{154}$Sm nucleus.

To first determine the ratio of cross sections for elastic photon scattering versus Smekal-Raman scattering to the first excited state of the ground-state rotational band in the strongly deformed nucleus $^{164}$Dy, a similar nuclear resonance fluorescence experiment was conducted on the GDR of $^{164}$Dy in 2023.
$^{164}$Dy is of particular interest due to its suspected higher degree of triaxiality. Experimental $\gamma$-ray spectra, the current status of the data analysis, and first results will be presented.

This work is supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 499256822 – GRK 2891 'Nuclear Photonics' and by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Grants No. DE-FG02-97ER41041 (UNC), and No. DE-FG02-97ER41033 (Duke, TUNL).

[1]J. Kleemann et al., Phys. Rev. Lett. 134, 022503 (2025)

Speaker: Marc Heumüller (Institut für Kernphysik, TU Darmstadt)

Oslo2026Talk.pdf

15:40 Photonuclear excitation of 26Mg and particle emission on PANDORA project.

The PANDORA experiment, conducted in October last year in RCNP, delves into photo-nuclear reactions within the mass region below A ∼ 56. This project aims to unravel the energy loss process of ultra-high-energy cosmic rays (UHECRs) during inter-galactic propagation. The origin, acceleration mechanism, and composition of UHECRs remain mysteries. Nonetheless, cosmic-ray air-shower observatories such as Pierre Auger and Telescope Array have detected UHECRs with energies above 1020eV. Analysis of air-shower depth distributions revealed a trend to heavier in the mass composition between protons and iron at the highest energies.
UHECR nuclei are anticipated to predominantly loss their energy by emitting particles after photo-nuclear excitation induced by absorbing cosmic microwave background (CMB) photons. Consequently, understanding photonuclear reaction cross-sections and decay branching ratios assumes paramount importance in understanding the energy and mass loss process of UHECRs during inter-galactic propagation.
The experiment employed virtual photon exchange via proton scattering to excite target nuclei and determine the photo-absorption cross-sections covering the giant dipole resonance. Detection of decay particles will extract branching ratios.
I will report the experiment's setup in October 2025 and outline the status of the analysis for 26Mg.

Speaker: Yusuke Irie (The University of Osaka)

Oslo Workshop.pdf

16:00 → 16:30 Coffee

16:30 → 18:30 Discussion session: Gamma Strength Function

Convener: Mathis Wiedeking (Lawrence Berkeley National Laboratory)

Oslo2026_gsf_discussion.pdf

Oslo2026_gsf_discussion.pptx

Thursday 21 May

08:30 → 09:00 Coffee

09:00 → 10:40 Breakfast session

Convener: Atsushi Tamii

09:00 Radiative strength functions from the energy-localized Brink-Axel hypothesis

Radiative strength functions (RSFs) model the bulk electromagnetic response of highly-excited nuclei and are critical inputs for statistical reaction codes. In this talk, I present a definition of the RSF that is consistent with Hauser-Feshbach reaction codes and that can be efficiently computed with the shell model by taking advantage of the energy-localized Brink-Axel hypothesis.

Speaker: Oliver Gorton (Lawrence Livermore National Laboratory)

09:30 Direct Neutron Capture Measurements with a Storage Ring

Neutron capture reactions are fundamental to understanding the synthesis of elements heavier than iron in stellar environments, occurring through the slow (s), intermediate (i), and rapid (r) neutron‑capture processes. While neutron‑capture cross sections along the valley of stability—particularly for stable or long‑lived isotopes—have been extensively studied, direct measurements on short‑lived nuclides (T₁/₂ ≪ 1 year) remain inaccessible with current techniques.

Heavy‑ion storage rings coupled to radioactive‑beam facilities provide a powerful platform for advancing such studies. Over the past decade, the ESR and CRYRING at GSI Darmstadt have enabled inverse‑kinematics measurements of astrophysically relevant reaction rates, though to date only for charged‑particle reactions. With the NRING project at CRYRING [1], we propose the first facility capable of performing direct neutron‑capture measurements on shorter-lived isotopes.

In this contribution, I will outline the NRING concept and discuss its expected capabilities and limitations. Ultimately, fully harnessing this new approach will require the development of a dedicated future “neutron‑capture storage ring” integrated with an ISOL facility—an advancement that could enable hundreds of direct neutron‑capture measurements on short‑lived nuclei down to half-lives of seconds in the coming decade.

[1] Ariel Tarifeño-Saldivia, César Domingo-Pardo, Iris Dillmann, Yuri A. Litvinov, "Direct Neutron Reactions in Storage Rings Utilizing a Supercompact Cyclotron Neutron Target", https://arxiv.org/abs/2508.15465, subm. to Phys. Rev. Acc.and Beams (2026)

Speaker: Iris Dillmann

Oslo2026_Dillmann_public.pdf

10:00 Microscopic Nuclear Level Densities and Giant Dipole Response within Covariant Energy Density Functional Theory

Nuclear level densities (NLDs) and the giant dipole resonance (GDR) encode complementary aspects of nuclear many-body dynamics and provide the microscopic structural input for compound-nucleus reactions. A consistent microscopic description of both quantities within a unified relativistic framework remains essential for understanding their structural origin and predictive power.

In this contribution, we present a systematic study of GDR properties within covariant density functional theory (CDFT). The electric dipole response is calculated using the relativistic quasiparticle random phase approximation (RQRPA) built on self-consistent relativistic Hartree–Bogoliubov (RHB) ground states. From the resulting E1 strength distributions, global GDR parameters are extracted across isotopic chains. In order to facilitate a direct comparison with experimental photoabsorption data, a tiny smearing approximation （TSA) method is employed, preserving the microscopic structure of the response while accounting for the finite width of the resonance. The deformation dependence and shell evolution of the dipole strength are analyzed in a fully self-consistent manner.

Microscopic nuclear level densities are constructed within the RHB+combinatorial framework based on the underlying quasiparticle spectra. This approach allows us to investigate in detail the impact of pairing correlations and shell structure on the excitation spectrum, in particular the role of quasiparticle gaps and their evolution with neutron number and intrinsic deformation.

Finally, the microscopic GDR parameters and level densities derived from the same CDFT framework are implemented as structure-based inputs to statistical reaction calculations. This unified treatment establishes a coherent link between intrinsic quasiparticle dynamics, collective dipole response, and reaction observables, providing a microscopic foundation for nuclear reaction modeling in medium and heavy nuclei.

Speaker: yuan tian (China institute of atomic energy)

oslo-TianYuan.pdf

oslo-TianYuan.pptx

10:20 Measurements and Modeling of $^{93}$Nb(n,xn$\gamma$)

A good understanding of Neutron-induced reactions on niobium are important for modeling radiation damage in superconducting magnets used in fusion energy systems and for interpreting archival radiochemical data for national security[1][2]. In order to constrain model parameters used in evaluation, correlated measurements of outgoing neutrons and gammas were collected using the Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) [3]. A 23 MeV deuteron beam was impinged onto a carbon target to generate a broad energy neutron beam at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory[4]. A natural Nb target was positioned at the center of the GENESIS array located 7 m downstream from the carbon breakup target. At the time of the experiment GENESIS consisted of 26 liquid organic scintillators for neutron detections and 3 high purity germanium detectors for gamma detection.

This talk will provide an overview of the analysis method using collected neutron and gamma data for reaction model optimization. It will also describe the method used to reproduce the observables measured in the experiment using a characterized array response and a reaction modeling code. The Hauser-Feshbach code CoH3 was used for reaction modeling[5]. The modeling process was applied iteratively in order to provide a set of optimized reaction model parameters in a similar manner to the nuclear data evaluation process but using only a single data set used to constrain several reaction channels.

[1] D. R. Nethaway. “THE 93Nb(n,2n) 92m92Nb CROSS SECTION”. In: Journal of L Inorganic and Nuclear Chemistry. (1977).
[2] D. R. Nethaway and M. G. Mustafa. “Measured Data Used in the Watusi Cross-Section Sets”. In: National Technical Information Service
(1999).
[3] J.M. Gordon et al. “GENESIS: Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering”. In: Nuclear Instruments and Methods
in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1061 (2024), p. 169120. issn: 0168-9002. doi:
https://doi.org/10.1016/j.nima.2024.169120. url: https://www.sciencedirect.com/science/article/pii/S0168900224000469.
[4] J. T. Morrell et al. “Secondary neutron production from thick target deuteron breakup”. In: Phys. Rev. C 108 (2 Aug. 2023), p. 024616.
doi: 10.1103/PhysRevC.108.024616. url: https://link.aps.org/doi/10.1103/PhysRevC.108.024616.
[5] T. Kawano. “CoH3: The Coupled-Channels and Hauser-Feshbach Code”. eng. In: Compound-Nuclear Reactions. Springer Proceedings in
Physics. Cham: Springer International Publishing, 2020, pp. 27–34. isbn: 3030580814. doi: 10.1007/978-3-030-58082-7_3.

Speaker: Keenan Myers

KM_2026_Oslo_Talk.pptx

10:40 → 11:10 Coffee

11:10 → 12:20 Midday Session

Convener: Lee Bernstein

11:10 Neutron transmission as a surrogate to tightly constrain neutron capture rates on radionuclides

Th. Stamatopoulos, P. Koehler, A. Cooper, A. Couture, B. DiGiovine, T. Morrow, E. Renner, J. Svoboda

Los Alamos National Laboratory, 87545, NM, USA

With very few exceptions, direct measurements of neutron capture rates on radionuclides have not been possible. A number of indirect methods have been pursued such as the surrogate method [1], the γ-ray strength function method [2,3], the Oslo method [4-7] and the β-Oslo method [8]. Substantial effort has been devoted to quantifying the usually large systematic errors that accompany the results from these techniques. A new instrument has been recently developed at the Los Alamos Neutron Science CEnter (LANSCE) to provide more accurate data on several radionuclides relevant to nuclear criticality safety, radiochemical diagnostics, astrophysics, nuclear forensics and nuclear security, by measuring the transmission of neutrons through radioactive samples and studying resonance properties. The Device for Indirect Capture on Radionuclides (DICER) [9-11] and associated radionuclide production at the Isotope Production Facility (IPF) [12, 13], both at LANSCE, as well radioactive sample fabrication, have been under development the last few years. A description of the apparatus, technique and some published data [14, 15] will be presented.

References
1. J. E. Escher et al., Phys. Rev. Lett. 121, 052501 (2018)
2. H. Utsunomiya et al., Phys. Rev. C 82, 064610 (2010)
3. H. Utsunomiya et al., Phys. Rev. C 88, 015805 (2013)
4. M. Guttormsen et al., Nucl. Instrum. Meth. A, 374 (3) (1996)
5. M. Guttormsen et al., Nucl. Instrum. Meth. A, 255 (3) (1987)
6. A. Schiller et al., Nucl. Instrum. Meth. A, 447 (3) (2000)
7. A. C. Larsen et al., Phys. Rev. C 83, 034315 (2011)
8. A. Spyrou et al., Phys. Rev. Lett. 113, 232502 (2014)
9. P.E. Koehler, Springer Proceedings in Physics, 254 (2021) p. 187
10. P.E Koehler, LA-UR-18-22995 (2018)
11. A. Stamatopoulos et al., Nucl. Instrum. Meth. A, 1025 (2022) 166166
12. K.F. Johnson et al., LA-UR-04-4570 (2004)
13. https://lansce.lanl.gov/facilities/ipf/index.php
14. A. Stamatopoulos et al., Phys. Rev. Lett. 134, 112702 (2025)
15. A. Stamatopoulos et al., Phys. Rev. C 111 034613 (2025)

Speaker: Thanos Stamatopoulos (Los Alamos National Laboratory)

Oslo2026_Thanos_DICER.pptx

11:40 Investigating the low-energy enhancement in Zr isotopes

Systematic measurements of the γ-ray strength function have shown a strong change of the low-energy enhancement (LEE) as a function of nuclear deformation. In an attempt to explore this behavior further, we performed a series of experimental studies in neutron-rich Zr isotopes, namely $^{97-100}\mathrm{Zr}$. These isotopes are in a region of abrupt deformation change from mostly spherical to highly deformed. As such, they are ideal for further exploring the deformation-dependence of the LEE. The experiments took place at the Argonne National Laboratory using the CARIBU facility. The nuclei of interest were populated using the $\beta$ decay of $^{97-100}\mathrm{Y}$ isotopes and the SuN total absorption spectrometer was used to measure the emitted $\gamma$ rays. We used the $\beta$ Oslo method to simultaneously extract the Nuclear Level Density and $\gamma$-ray Strength Function for each isotope. In this talk I will present first surprising results on these systematics studies.

Speaker: Artemis Spyrou

Spyrou-Oslo2026.pdf

Spyrou-Oslo2026.pptx

12:00 Oslo studies near $^{92}$Nb and the implications for Stellar Production of the Cosmochronometer $^{92}$Nb

The extinct radionuclide $^{92}$Nb (half-life $\sim$ 34.7 Myr) is a sensitive tracer of proton-rich nucleosynthesis and a chronometer for the early Solar System. Interpretation of meteoritic $^{92}$Nb/$^{92}$Mo ratios is currently limited by both astrophysical and nuclear-physics uncertainties. In particular, the origin of $^{92}$Nb remains uncertain because it is shielded by the stable isobars $^{92}$Zr and $^{92}$Mo and therefore must be synthesized through direct nuclear reactions in explosive supernova environments. The $^{91}$Nb($n$,$\gamma$)$^{92}$Nb reaction rate is among the most influential inputs for the production of $^{92}$Nb under such conditions. However, due to the instability of $^{91}$Nb, direct measurements of the $^{91}$Nb($n$,$\gamma$)$^{92}$Nb cross section and thus the reaction rate are not currently feasible. As a result, recommended rates in commonly used libraries rely heavily on Hauser-Feshbach calculations, whose accuracy depends on nuclear statistical properties, such as the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF) of $^{92}$Nb, for which no experimental constraints have previously been available. Here, we report an experimental constraint on the $^{91}$Nb($n$,$\gamma$)$^{92}$Nb rate by extracting the NLD and $\gamma$SF of $^{92}$Nb using the Oslo method applied to particle-$\gamma$ coincidences measured in the $^{90}$Zr($\alpha$,d$+\gamma$)$^{92}$Nb reaction at the Oslo Cyclotron Laboratory using a $^{4}$He beam at 30 MeV, with the SiRi particle telescope in coincidence with the OSCAR LaBr$_3$(Ce) array. The extracted NLD and $\gamma$SF were propagated through Hauser-Feshbach calculations with TALYS to obtain an experimentally constrained $^{91}$Nb($n$,$\gamma$)$^{92}$Nb reaction rate. The resulting band is a factor of $\sim$ 2-3 below the recommended NON-SMOKER rate over the supernova relevant temperature window. The astrophysical impact of the improved rate was evaluated using NuGrid one-zone post-processing calculations for core-collapse and thermonuclear supernova conditions. The results show that the yield response can differ in sign between stellar environments, demonstrating that a single experimentally constrained reaction rate can shift inferred $^{92}$Nb production and, consequently, early Solar System chronology, highlighting the leverage of Oslo-type inputs for reducing nuclear uncertainties in proton-rich nucleosynthesis. An independent verification of the $^{91}$Nb($n$,$\gamma$)$^{92}$Nb reaction rate is also planned through extraction of the NLD and $\gamma$SF of $^{92}$Nb using the Charge-Exchange (CE) Oslo method, which will be applied to particle-$\gamma$ coincidence data from the planned $^{92}$Zr($^{3}$He,t$+\gamma$)$^{92}$Nb experiment at RCNP using a 420 MeV $^{3}$He beam, with the Grand Raiden spectrometer in coincidence with a scintillation $\gamma$-ray detector array. The CE-Oslo method was first tested using $^{93}$Nb($t$,$^{3}$He$+\gamma$) data taken with the S800 spectrometer in coincidence with the GRETINA $\gamma$-ray detector at the National Superconducting Cyclotron Laboratory (NSCL). Using the constructed particle-$\gamma$ coincidence matrix for $^{93}$Zr, the NLD and $\gamma$SF of $^{93}$Zr were extracted and then propagated through Hauser-Feshbach calculations with TALYS to estimate the $^{92}$Zr($n$,$\gamma$)$^{93}$Zr cross section. The resulting cross section is in good agreement with direct measurements, thereby validating the CE-Oslo method, and has been published as its first demonstration.

This research is supported by the U.S. National Science Foundation (NSF), the Norwegian Nuclear Research Center (NNRC), and the International Research Network for Nuclear Astrophysics (IReNA).

[1] A.C. Larsen et al., Phys. Rev. C 83 (2011) 034315.
[2] N.D. Pathirana et al., Phys. Rev. C 113 (2026) 015801.
[3] M. Lugaro et al., Proc. Natl. Acad. Sci. U.S.A. 113 (2016) 907-912.
[4] A. Koning, S. Hilaire, S. Goriely, Eur. Phys. J. A 59 (2023) 131.
[5] R.H. Cyburt et al., Astrophys. J. Suppl. Ser. 189 (2010) 240-252.
[6] F. Herwig et al., PoS NIC X 053 (2009) 023.
[7] M. Pignatari, F. Herwig, Nuclear Physics News 22 (2012) 18-23.

Speaker: Neshad Deva Pathirana (Facility for Rare Isotope Beams - Michigan State University)

Oslo_workshop_2026.pdf

Oslo_workshop_2026.pptx

12:20 → 14:30 Lunch break

14:30 → 18:00 Collaboration discussions/Free time

18:00 → 22:00 Workshop dinner

Friday 22 May

08:30 → 09:00 Coffee

09:00 → 11:00 Breakfast session

Convener: Dennis Muecher (Institute for Nuclear Physics, University of Cologne)

09:00 Fission with PARIS@VAMOS: At the crossroad between nuclear dynamics and nuclear structure

As obvious from the intense experimental and theoretical work done over the past decades, and the still large amount of open questions, nuclear fission is a particularly complex process. A major reason for this is the interference of various aspects, from both reaction dynamics and nuclear structure, which determines the observables that can be measured in the laboratory. The last years showed that high-fold coincidences between as many as possible observables are crucial to unravel the intricacies of fission, a mandatory condition for unambiguous interpretation. In this context, an innovative experimental approach was set up at GANIL coupling for the first time a heavy-ion spectrometer such as VAMOS++ and a new generation scintillator array like PARIS. While the former is capable of identifying accurately in mass and charge the fragments emitted in fission, the latter gives access to the properties of the coincident $\gamma$ rays over their full dynamical range with unprecedented quality, as well as information about the coincident neutrons. In this contribution, the first experiment with PARIS@VAMOS dedicated to fission induced by fusion and nucleon transfer in $^{238}\mathrm{U}+^{9}\mathrm{Be}$ collisions is presented. A selection of results is used to illustrate the performance and sensitivity of the approach. The so-called fission $\gamma$ bump and its highly likely connection to the Pygmy Dipole Resonance are discussed by means of calculations employing microscopic nuclear level densities and $\gamma$ strength functions. The impact of this connection is double, as it makes the $\gamma$ bump a relevant signature of the dynamics after scission, as well as it proposes fission as a new probe of soft dipole modes, complementary to conventional approaches.

Speaker: C. Schmitt (Institut Pluridisciplinaire Hubert Curien, France; Institute of Nuclear Physics Polish Academy of Sciences)

09:30 Fission cross sections and nuclear level densities

Despite nearly 90 years since its discovery, the fission process remains a challenge for nuclear theories. Three main aspects have to be contemplated: the fission cross sections (probability that a fission occurs), the fission yields (distribution of the fragments resulting from the scission of the fissioning nucleus) and the fission fragments’ decay (responsible in particular of the prompt neutrons involved in the chain reaction).
Even if these three aspects are subject to important theoretical developments, this talk will focus on the calculation of the fission cross sections with a particular attention paid to the role played by nuclear level densities in the reaction modeling.

Speaker: Stephane Hilaire (CEA, DAM, DIF)

10:00 Nuclear fission - experiments and modeling

This presentation provides an overview of recent experimental advances in nuclear fission research at the NNRC. We begin by summarizing key results from fission yield measurements performed at the Institut Laue Langevin, together with investigations of isomeric yield ratios obtained using the Nuball detector array. These studies contribute to a more detailed understanding of fragment mass formation mechanisms and nuclear structure effects in fission.
We then discuss recent developments in fission modeling, with particular emphasis on the role of TALYS as a unifying framework. Recent progress has positioned TALYS at the center of efforts to integrate databases generated by a range of fission models, enabling consistent treatment of fragment de excitation through the Hauser Feshbach statistical formalism. This approach lead to predictive and internally consistent calculations of post fission observables.
We highlight ongoing work aimed at incorporating data from the FREYA code into this framework, with the goal of expanding the range of available input distributions and improving model versatility. In addition, a validation study is discussed in which calculated isomeric yield ratios with TALYS are systematically compared with results obtained using the Manchester spin method. This comparison serves as an important benchmark for assessing the reliability of spin population modeling within the combined TALYS based approach.

Speaker: Ali Al-Adili

presentation_AlAdili2.pdf

10:20 Measurements of Partial Gamma Ray Production Cross-sections from U-238 Inelastic Scattering

Improved measurements of $^{238}U(n,n'\gamma)$ cross-sections are needed to refine nuclear data evaluations used for fast reactors, stockpile stewardship, and nuclear astrophysics. The preliminary results of an experiment to measure neutron inelastic scattering on a natural uranium target will be presented. A 14 MeV deuteron beam was used to create a pulsed broad spectrum neutron beam via thick target deuteron breakup on carbon at the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory. The outgoing gammas and neutrons were measured simultaneously using the Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS). GENESIS is equipped with high purity germanium detectors and liquid organic scintillators that are capable of particle discrimination to isolate neutrons. Together they allow for high-resolution correlated neutron-gamma measurements to be made. The beam's pulse period leads to frame overlap of consecutive pulses where multiple neutron energies impinge on the target at the same time. This makes observations of $\gamma$ yields a convolution over multiple neutron energies. To resolve this, a reaction model code is coupled directly to our measured data through a modeled response matrix to allow for prediction of measured quantities. The reaction modeling parameters are then optimized using $\chi^2$ minimization to obtain a best fit of the reaction model inputs which include level density, gamma strength, and neutron optical model parameters. The measurements and modeling results will be presented as well as future work being done on the GENESIS array to further study fission in $^{238}U$.

Speaker: Speero Tannous

Tannous_OsloSlides_v2.pptx

10:40 Fission Program at the Oslo Cyclotron Laboratory: Upcoming Setup and Goals

Nuclear fission remains one of the most complex processes in low-energy nuclear physics, with some open questions spanning both fundamental nuclear structure and applied nuclear technology. To address these challenges, the Oslo Cyclotron Laboratory (OCL) at the University of Oslo is establishing a dedicated fission research program that exploits its unique combination of light-ion beams and advanced instrumentation.

At the centre of this initiative is a newly designed experimental setup integrating scintillation-based fission fragment detectors [3, 4] with the high-efficiency OSCAR gamma-ray array [1, 2], enabling event-by-event coincidence measurements between fission fragments and prompt gamma rays. The OCL’s capability to deliver proton, deuteron, and alpha beams makes it ideally suited for particle-induced fission studies on actinide targets, allowing systematic variation of excitation energy and fissioning nucleus. Earlier measurements using conventional ionization-based gas detectors and the SiRi charged-particle telescope [5] demonstrated clear signatures of nuclear structure effects in the prompt fission gamma-ray spectrum (PFGS) and their sensitivity to excitation energy [6]. Building on this foundation, the program is advancing toward deployment of highly segmented S2 silicon detectors for charged-particle identification, which will deliver improved excitation-energy resolution and open new avenues for spectroscopic studies in fissioning systems.

The integration of multi-detector coincidence arrays with modern data acquisition and offline analysis routines will enable stringent constraints on theoretical fission models, with implications for both fundamental nuclear physics and reactor-relevant applications. This contribution will present the scientific motivation and experimental strategy of the OCL fission program and the status of the detector commissioning.

References
[1] F. Zeiser, et al., Nucl. Instrum.Meth. A 985, (2021) 164678.
[2] V. W., Ingeberg et al., Under production and soon to be submitted.
[3] M. Hunyadi et al., Adv. Photonics Res. 2025, 2400217.
[4] M. Hunyadi et al., Adv. Funct. Mater. 2022, 32, 2206645
[5] M. Guttormsen et al., Nucl. Instrum. Methods Phys. Res. A 648, (2011) 168–173.
[6] D. Gjestvang et al., Phys. Rev. C 103, (2021) 034609.

Speaker: Neeraj Kumar (Norwegian Nuclear Research Centre (NNRC), University of Oslo)

11:00 → 11:20 Coffee

11:20 → 13:10 Midday Session

Convener: Paraskevi Dimitriou (International Atomic Energy Agency)

11:20 PANDORA Project: Charged Particle Decay from the IVGDR in 27Al

The study of photo-nuclear reactions is crucial for understanding nuclear structure and astrophysical processes. The PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project [1] aims to systematically investigate these reactions in stable nuclei with mass numbers below 60. We use virtual photon exchange through proton scattering at RCNP. The subsequent decay particles and gamma-rays are detected to measure the photo-absorption cross-section and the decay branching ratio for each decay channel, covering the giant dipole resonance.
The primary objective of the PANDORA project is to elucidate the energy loss mechanisms of ultra-high-energy cosmic ray (UHECR) nuclei during intergalactic propagation. UHECRs are observed on Earth up to energies above 1020 eV by large cosmic-ray air-shower observatories such as Pierre Auger and Telescope Array They remain a mystery in terms of origin, acceleration mechanisms, and composition. Recent analyses suggest a heavier mass composition for UHECRs at the highest energies. UHECR nuclei are predicted to lose energy primarily by emitting particles following photo-nuclear excitation by cosmic microwave background photons. Thus, understanding photonuclear reaction cross-sections and decay branching ratios is essential for interpreting the energy and mass evolution of UHECRs.
I will introduce the project, experimental method at RCNP [2] and the preliminary result of the charged particle decay of IVGDR in 27Al.

References
[1] A. Tamii et al., PANDORA White Paper, Euro. Phys. J. A. 59, 208 (2024).
[2] P. von Neumann-Cosel and A. Tamii, Euro. Phys. J. A 55, 110, (2019)

Speaker: Atsushi Tamii

Oslo2026_Tamii_v5.pdf

11:50 Statistical properties of 143Ba

The nucleosynthesis of approximately half of the elements heavier than iron is attributed to the r-process. A key input for modeling the r-process is the neutron-capture cross-section of neutron-rich nuclei. However, astrophysical sensitivity studies suggest that uncertainties in these cross-sections significantly impact the predicted abundances. In particular, in the A=140 region, calculations underproduce the observed abundances by nearly an order of magnitude. The main sources of uncertainty in neutron-capture cross-sections calculations come from the Nuclear Level Density (NLD) and Gamma-Ray Strength Function ($\gamma$SF).

Here, we present the results from the analysis of $^{142}\text{Ba}(n,\gamma)^{143}\text{Ba}$ using the $\beta$-Oslo method. The compound nucleus $^{143}\text{Ba}$ was populated via $\beta$-decay of $^{143}\text{Cs}$ beams at the Argonne National Laboratory. The emitted $\gamma$-rays were detected using the segmented total absorption calorimeter: the Summing NaI(Tl) (SuN) detector. The segmented scintillator allows us to measure the individual $\gamma$-rays as well as the excitation energy of the populated states in the compound nucleus. Using the $\beta$-Oslo method, we extract the NLD and $\gamma$SF of $^{143}\text{Ba}$, which are then used to constrain the neutron-capture cross-section. The results of the NLD and $\gamma$SF will be presented.

Speaker: Hershini Gadaria (Michigan State University)

oslo_final_hershini.pptx

12:10 Microscopic study of the low-energy enhancement in the gamma-decay strength of $^{50}$V

The low-energy enhancement (LEE) of the dipole γ-ray strength function has been observed in many nuclei, yet its microscopic origin remains debated. We investigate the LEE in $^{50}$V using large-scale shell-model calculations that treat electric and magnetic dipole transitions consistently within a single framework. Calculations are performed in a sd–pf–sdg valence space with a $1\hbar\omega$ truncation, employing the SDPFSDG-MU interaction and the KSHELL code. The model space yields several thousand eigenstates and nearly two million individual E1 and M1 transitions.

Benchmark comparisons demonstrate excellent agreement with experimental data: low-lying levels are reproduced within 300 keV, the calculated level density matches Oslo-method data up to $E_x\!\approx\!7.5$ MeV, and the dipole γ-strength function follows the measured shape over the full experimental γ-energy range, including the LEE. By separating electric and magnetic contributions, we show that the enhancement in $^{50}$V is entirely of magnetic dipole origin. Both spin and orbital components of the M1 operator are essential, with constructive interference between them providing a significant additional enhancement at low γ energies.

Analysis of one-body transition densities identifies $0f_{7/2}\!\rightarrow\!0f_{7/2}$ proton transitions as the dominant microscopic mechanism driving the LEE, while transitions between different orbitals govern the higher-energy M1 strength. These results establish a direct link between specific shell-model configurations and emergent statistical properties of γ decay, providing a quantitative microscopic explanation of the LEE in this mass region.

Speaker: Jon Kristian Dahl (University of Oslo)

2026-05-18_oslo_nld_gsf_workshop.pdf

12:30 First results on the direct determination of the 12C+12C reaction at LUNA

Carbon burning is the third stage of stellar evolution, determining the fate of both massive stars and low-mass stars in binary systems.
Only stars with a mass larger than a critical value M∗ up ∼ 10M⊙, can ignite Carbon in non-degenerate conditions and proceed to the next advanced burning stages up to the formation of a gravitationally unstable iron core.
Various final destinies are possible, among which a direct collapse into a black hole or the formation of a neutron star followed by the violent ejection of the external layers (type II SN).
Less massive stars M < Mup ∼ 7M⊙, never attain the conditions for C ignition and will evolve into CO White Dwarfs.
The values of M∗ up and Mup depend on the 12C + 12C reaction rate, which remains uncertain at astrophysical energies.
Stellar Carbon burning occurs mainly through the 12C(12C, α)20Ne and 12C(12C, p)23Na reactions.
These cross-sections can be measured either by detecting the emitted charged particles
or the γ-rays produced by the decay excited states of 20Ne and 23Na.

The 12C + 12C fusion reactions were investigated across a broad energy range.
However the lowest energy reached by direct measurement is 2.1 MeV, still above astrophysical energies.
Indirect data obtained with methods such as the Trojan Horse approach are available at astrophysical energies,
but suffer from uncertainties in the renormalization.
Direct measurements are thus essential for both stellar evolution models and the interpretation of indirect data.
In this context, a direct study is currently being carried out by the LUNA collaboration at the Bellotti ion beam facility in the deep underground laboratories of the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, where intense carbon beams with energies up to 7 MeV and excellent energy resolution and stability are available.
The objective of this measurement is to directly determine the 12C+12C cross-section at astrophysical energies by γ spectroscopy.
The detection setup is made of several NaI scintillators surrounding a 150% HPGe in a compact configuration, covering
~3.5π steradians.
This configuration ensures high efficiency and preserves the
HPGe resolution (1.2 keV at 1.33 MeV).
The NaI setup will also act as an active veto for Compton, environmental, and beam-induced background.
The detectors are placed in side a 2cm copper shielding surrounded by a 25cm lead shielding,
which will further reduce the environmental background at LNGS of over two orders of magnitude.
This setup will allow us to achieve unprecedented sensitivity,
with an expected background about four orders of magnitude lower than the previous direct measurements that reached the lowest energies.

With this setup, we'll be able to shed light on the level density of 24Mg through the de-excitation of 20Ne and 23Na nuclei.
This will allow us to explore the possible cluster structures of the 24Mg nucleus.
In particular, we'll be able to examine the E_cm = 1.5 MeV - 3.5 MeV energy
window (15.44 MeV to 17.44 MeV considering the Q-value), where the cluster states could be found.
Those states will determine the rate of the 12C+12C at astrophysical energies.

With my contribution I will present details of recent results setup development and installation,
together with Geant4 simulations and a detailed characterization of the HPGe detector active volume.
I will also present preliminary results of the first beam-on-target devoted to
the direct measurement of the 12C+12C reaction at energies E_cm > 2 MeV .

Speaker: Riccardo Maria Gesuè (Gran Sasso Science Institute, INFN LNGS)

Gesue_12C12C.pdf

12:50 Investigation of $^{24}$Mg nuclear structure in the energy range relevant to carbon-burning in stars

The nuclear structure of $^{24}$Mg in the excitation energy region relevant to the $^{12}$C+$^{12}$C fusion reaction is crucial for constraining carbon-burning processes in massive stars. Although this reaction has been extensively studied over the past decades, significant uncertainties persist, particularly at center of mass energies below 2.5 MeV, where direct measurements are hindered by extremely low cross sections. In this context, indirect approaches providing detailed spectroscopic information on the compound nucleus $^{24}$Mg are essential.

In this contribution, we present a new dedicated experiment to be performed at the Oslo Cyclotron Laboratory (OCL) to investigate the excited states of $^{24}$Mg in the energy range 14-17 MeV via $\alpha$ inelastic scattering. Reaction products will be detected in coincidence using the Oslo Scintillator Array (OSCAR), the SiRi particle telescope, and the INFN OSCAR silicon hodoscope. The combined use of charged-particle and $\gamma$-ray spectroscopy will enable a reliable determination of the spin and parity of the populated states in $^{24}$Mg, as well as an estimate of the branching ratios of its decay channels.

Speaker: Federica Ercolano (Università degli Studi di Napoli Federico II, INFN Sezione di Napoli)

OsloWorkshop2026_Ercolano.pptx

13:10 → 14:30 Lunch Break

14:30 → 16:00 Afternoon session

Convener: Alexander Voinov (Ohio University)

14:30 Surrogate Reaction Theory: Recent Developments and Applications

The surrogate reaction method offers a powerful alternative to direct measurements of compound nuclear reaction cross sections but relies critically on theory developments for modeling the surrogate reaction used to populate the compound nucleus of interest. In this talk, I will present recent theoretical extensions for proton inelastic scattering and (d,p) surrogate reactions. This includes connecting microscopic structure of the compound nucleus to surrogate reaction theory, and examining the role of Porter-Thomas fluctuations in surrogate reaction modeling. Microscopic structure theory calculations of Pygmy and toroidal dipole resonances, relevant to E1 gamma-ray strength functions, will also be discussed.

Speaker: Aaina Thapa (Lawrence Livermore national Laboratory)

15:00 The measurement of gamma-decay in photo-nuclear reaction on 12C、13C、27Al for the PANDORA project

Photo-nuclear reaction on light nuclei (A<60) is important to understand extragalactic propagation of cosmic-rays with energy greater than 1018 eV, but theoretical models of photo-nuclear reactions on these nuclei have been facing challenges due to lack of experimental data. PANDORA project aims at extracting these data such as photo-absorption cross section, E1 strength and branching ratios for particle decay. The experiment using virtual photon method has been done at RCNP in 2023 and 2025, and will be carried out at iThemba LABS. It is also planned to have an experiment using laser compton back scattering gamma beam at ELI-NP. In the experiment at RCNP, the Grand Raiden spectrometer was used combined with silicon detector for charged particle decay measurement and LaBr3 detectors for gamma decay measurement. 392 MeV proton beam was used to excite the target nucleus with forward angle inelastic scattering. Once a nucleus excited to GDR, particle decay happens and gamma decay on daughter nucleus is measured. Although the probability is very low (~ 1%), gamma decay on GDR might be measured with this set up. The preliminary results of gamma decay measurement on the 1st PANDORA experiment at RCNP will be presented.

Speaker: Yumaro Suzuki (RCNP, The University of Osaka)

Oslo Workshop 2026.5.22.pdf

Oslo Workshop 2026.5.22.pptx

15:20 Constraining the Xenon Poison Neutron Capture Rate for Reactor Design and Nuclear Safeguards

Measuring the $^{135}$Xe neutron-capture cross section ($^{135}$Xe($n,\gamma$)$^{136}$Xe) has been identified as a top priority for its role in reactor design, stockpile stewardship, nonproliferation, and astrophysics [1]. Current cross section data does not extend above thermal neutron energies and data evaluations differ by an order of magnitude. Performing direct neutron-capture measurements on unstable nuclei is challenging, making it necessary to rely on indirect measurements that utilize the statistical properties of nuclei, namely the nuclear level density and gamma-ray strength function. These quantities are used as inputs for Hauser-Feshbach reaction calculations that ultimately provide neutron-capture constraints. However, the predicted statistical properties exhibit large theoretical uncertainties themselves and need to be better constrained for more accurate predictions. This work focuses on experimentally constraining the non-thermal $^{135}$Xe neutron-capture rate by simultaneously extracting the aforementioned statistical properties of $^{136}$Xe using two experimental methods. One experiment will use the $\beta$-Oslo method [2] to measure the $\beta$-decays of $^{136}$I and $^{136}$Te using the nuCARIBU facility at Argonne National Laboratory. The other will use the inverse-Oslo method [3] to measure inelastic proton scattering with the p($^{136}$Xe,$p’\gamma$)$^{136}$Xe reaction with DAPPER at Texas A&M University. Current development and preparation of these two experiments will be discussed along with preliminary results from the $\beta$-Oslo experiment.

This work was supported by the Office of Defense Nuclear Nonproliferation Research and Development within the U.S. Department of Energy’s National Nuclear Security Administration and performed under the auspices the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and Berkeley Lab under Contract AC02-05CH11231.

References:
[1] Root, S. J. et al. (2023) Nuclear Engineering and Design, 414, 112606.
[2] Spyrou, A. et al. (2014) Phys. Rev. Lett., 113, 232502.
[3] Ingeberg, V. W. et al. (2020) Eur. Phys. J. A., 56, 68.

Speaker: Austin Rambo (Ohio University)

136Xe_Oslo_presentation.pptx

15:40 Nuclear Data for Medical Applications

Speaker: Andrew Voyles

16:00 → 16:10 Closing talk